JAMB UTME - Physics - 2018

The diagram shown represents a block-and-tackle pulley system on which an effort of W Newtons supports a load of 120.0N. If the efficiency of the machine is 40, then the value of W is?

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Let the total number of pulleys used in both the blocks be $n$.
In a block-and-tackle pulley system, the velocity ratio is equal to n.
Efficiency = $\frac{\text{MA}}{\text{VR}}\times 100\%$
$\text{MA}=\frac{\text{L}}{\text{E}},\text{VR}=n$
Efficiency = $\frac{\text{L}}{\text{E}}\times \frac{1}{\text{n}}\times 100\%$
$\text{E}=\frac{\text{L}}{\text{Eff.}\times n}\times 100\%$
$\text{E}=\frac{120\text{N}}{40\%\times 6}\times 100\%$
$\text{E}=50\text{N}$

A man walks 1km due east and then 1 km due north. His displacement is

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The man first walks 1 km due east, which means he has moved 1 km horizontally to the right of his starting point. Then, he walks 1 km due north, which means he has moved 1 km vertically upwards from his previous position. To find his displacement, we need to draw a straight line from his starting point to his final position, which represents the shortest distance between the two points. This line is called the displacement vector. We can use the Pythagorean theorem to calculate the length of the displacement vector. The horizontal and vertical distances are the two legs of a right-angled triangle, and the hypotenuse is the length of the displacement vector. Using the Pythagorean theorem, we get: displacement = √((1 km)^2 + (1 km)^2) = √2 km The direction of the displacement vector is the angle between the displacement vector and the due north direction. We can find this angle using trigonometry. The tangent of the angle is the ratio of the horizontal distance to the vertical distance: tan(θ) = (1 km) / (1 km) = 1 Using a calculator, we can find that the angle is 45°. Therefore, the man's displacement is √2 km in the direction N 45° E. So, the correct answer is √2km N 45°E.

The resistance of a 40W car head lamp, drawing current from a 12V battery is ____.

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The resistance of a 40W car headlamp can be calculated using Ohm's Law, which states that the current (I) flowing through a conductor between two points is directly proportional to the voltage (V) across the two points, and inversely proportional to the resistance (R) of the conductor. The equation can be written as V = IR. Since the power (P) of the headlamp is given as 40W and the voltage is 12V, we can calculate the current using the equation P = IV. Substituting I = P/V, we get I = 40/12 = 3.33A. Finally, using Ohm's Law, we can calculate the resistance as R = V/I = 12/3.33 = 3.6Ω. So, the resistance of the 40W car headlamp, drawing current from a 12V battery, is 3.6Ω.

In a series R-L-C circuit at resonance, the voltages across the resistor and the inductor are 30V and 40V respectively. What is the voltage across the capacitor?

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Musical instruments playing the same note can be distinguished from one another owing to the difference in their

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Different musical instruments playing the same note can be distinguished from one another due to the difference in their "timbre" or "tone color." Timbre refers to the unique character or quality of a sound that allows us to distinguish it from other sounds even when they have the same pitch and loudness. For example, a piano and a guitar playing the same note will sound different due to the differences in their timbre. This is why we can tell the difference between different instruments and why some instruments are better suited to certain styles of music than others.

The electrochemical equivalent of silver is 0.0012g/C. If 36.0g of silver is to be deposited by electrolysis on a surface by passing a steady current for 5mins, the current must be?

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The electrochemical equivalent of silver is a measure of the amount of silver that is deposited on a surface per unit of charge. In this case, the electrochemical equivalent of silver is 0.0012 grams per Coulomb of charge. To deposit 36.0 grams of silver by electrolysis, we need to know the amount of charge that must be passed through the solution. The amount of charge is given by: Q = m/z where m is the mass of silver to be deposited, 0.0012 is the electrochemical equivalent of silver, and z is the charge on one mole of electrons (z = 1 for a single electron). So, the amount of charge required is: Q = 36.0 g / 0.0012 g/C = 30000 C The current, I, is given by: I = Q / t where t is the time for which the current is flowing. In this case, t = 5 minutes. So, the current required is: I = 30000 C / (5 x 60 s) = 100 A Therefore, the current must be 100 Amperes.

Which of the following has the lowest internal resistance when new?

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Among the given options, the Accumulator has the lowest internal resistance when new. Internal resistance is the resistance that a battery or cell provides to the flow of electric current within itself. Lower internal resistance means that the battery can supply more current to an external circuit without losing much of its own energy as heat. An Accumulator, also known as a rechargeable battery, is designed to be charged and discharged multiple times. It has a relatively low internal resistance when new, meaning it can provide a higher current than the other cells listed while wasting less energy internally as heat. A Leclanche cell and Daniell cell are primary cells, meaning they are designed to be used once and discarded. They have higher internal resistance compared to the accumulator, which limits their ability to supply high currents. A Torch battery, also known as a dry cell, is also a primary cell and has a higher internal resistance than the accumulator. It is commonly used in small electronic devices and has a longer shelf life than Leclanche and Daniell cells. In summary, an Accumulator has the lowest internal resistance when new, which makes it an ideal choice for applications requiring high current delivery such as electric vehicles, power tools, and renewable energy systems.

The density of 400cm3 of palm oil was 0.9gcm-3 before frying. If the density of the oil was 0.6gcm-3 after frying, assuming no loss of oil due to spilling, its new volume was?

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The density of a substance is defined as its mass per unit volume. Therefore, the mass of the palm oil before frying was: Mass = Density x Volume = 0.9 g/cm³ x 400 cm³ = 360 g After frying, the mass of the palm oil remains the same, but its density changes to 0.6 g/cm³. Therefore, the new volume of the palm oil can be calculated by rearranging the density formula: Volume = Mass / Density = 360 g / 0.6 g/cm³ = 600 cm³ So the new volume of the palm oil after frying is 600 cm³. is the correct answer.

Water of mass 150g at 60${}^o$c is added to 300g of water at 20${}^o$c and the mixture is well stirred. Calculate the temperature of the mixture.(neglect heat losses to the surroundings)

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To solve this problem, we can use the principle of conservation of energy, which states that energy cannot be created or destroyed, only transferred or converted from one form to another. In this case, the energy transferred is in the form of heat. We can use the formula: Q = m*c*(ΔT) where Q is the heat transferred, m is the mass of the water, c is the specific heat capacity of water, and ΔT is the change in temperature. First, we can calculate the heat transferred from the hot water to the cold water: Q1 = 150g * 4.18 J/(g°C) * (60°C - T) Q1 = 627 * (60 - T) where T is the temperature of the mixture. Next, we can calculate the heat transferred from the cold water to reach the final temperature of the mixture: Q2 = 300g * 4.18 J/(g°C) * (T - 20°C) Q2 = 1254 * (T - 20) Since the heat transferred between the two water samples must be equal, we can set Q1 equal to Q2 and solve for T: 627 * (60 - T) = 1254 * (T - 20) 37620 - 627T = 1254T - 25080 1881T = 62760 T = 33.4°C Therefore, the temperature of the mixture is approximately 33°C. Answer: 33°C

The efficiency of energy conversion on the energy flow through a hydroelectric power is?

Maelezo ya Majibu

Efficiency = $\frac{\text{useful energy output from machine}}{\text{energy input into machine}}$
= $\frac{E3}{E2}$

The linear expansivity of brass is 2 x 10${}^{?5}$ C${}^{?1}$. If the volume of a piece of brass is 15.00cm at 0°C, what is the volume at 100°C

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The linear expansivity of brass is given as 2 x 10^-5 /°C. This means that for every 1°C increase in temperature, the brass expands by 2 x 10^-5 of its original size. To find the new volume of the brass at 100°C, we need to take into account the expansion in all three dimensions (length, width, and height). Since the expansivity given is for length only, we need to find the expansivity in all three dimensions by multiplying it by 3. The expansivity in all three dimensions is: 3 x (2 x 10^-5 /°C) = 6 x 10^-5 /°C To find the new volume, we can use the formula: Vf = Vi (1 + αΔT) where Vf is the final volume, Vi is the initial volume, α is the expansivity in all three dimensions, and ΔT is the change in temperature. Plugging in the values, we get: Vf = 15.00 cm3 (1 + (6 x 10^-5 /°C) x (100°C - 0°C)) Vf = 15.09 cm3 Therefore, the volume of the brass at 100°C is 15.09 cm3.

A pulley system has three pulleys in the fixed block and two in the movable block and if the pulley has an efficiency of 72%, the mechanical advantage of the system is?

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To make it easier understood
MA = E × Vr/100
Vr in a pulley system is the number of pulleys and in this case we have 5 (3 and 2)
So
MA = 72 × 5 = 360/100 = 3.6
Thanks

A car traveled at a uniform speed of 100km/h, spends 15m moving from point A to point B along its route. The distance between A and B is

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To calculate the distance between point A and point B, we can use the formula: Distance = Speed x Time where the speed is given as 100 km/h and the time is given as 15 minutes, which we need to convert to hours. 1 hour = 60 minutes, so 15 minutes = 15/60 hours = 0.25 hours. Now, we can substitute these values into the formula: Distance = 100 km/h x 0.25 h = 25 km Therefore, the distance between point A and point B is 25 km. is the correct answer.

A boy receives the echo of his clap reflected by a nearby hill 0.8s later. If the speed of sound in air is 3.40ms${}^{-}1$, how far is he from the hill?

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The speed of sound in air is given as 3.40 m/s. The echo of the clap is heard 0.8 seconds after it was produced, which means it traveled to the hill and back. The time taken for sound to travel to the hill is half of the time taken for it to travel to and from the hill. Therefore, the time taken for sound to travel to the hill is 0.8/2 = 0.4 seconds. We can use the formula: distance = speed x time to calculate the distance between the boy and the hill. distance = speed of sound x time taken for sound to travel to the hill distance = 3.40 m/s x 0.4 s distance = 1.36 m Therefore, the distance between the boy and the hill is 1.36 meters. However, the answer options provided are in meters and are significantly larger than 1.36 meters. It is possible that the speed of sound provided in the question is incorrect or the answer options are incorrect.

A ball of mass 5.0kg hits a smooth vertical wall normally with a speed of 2ms${}^{?1}$. Determine the magnitude of the resulting impulse

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The magnitude of the resulting impulse can be calculated using the formula impulse = change in momentum. In this scenario, the ball experiences a change in velocity (speed) as it hits the wall. The ball's initial momentum is equal to its mass times its velocity, and its final momentum is zero since it comes to a stop after hitting the wall. The change in momentum is equal to the final momentum minus the initial momentum, which is equal to the negative of the initial momentum. Since the ball has a mass of 5.0 kg and a velocity of 2 m/s, its initial momentum is 5.0 kg * 2 m/s = 10.0 kg m/s. Therefore, the change in momentum is -10.0 kg m/s and the magnitude of the resulting impulse is 10.0 kg m/s, which is equal to 10.0 Ns. So, the correct answer is 10.0kgms−1.

A force of 5N acts at a point Y on a rod XYZ as shown in this diagram. If XYZ is 2m, what is the moment of the force about point X?

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To find the moment of the force about point X, we need to first understand what moment is. Moment is the turning effect of a force around a pivot point. It is calculated by multiplying the force by the perpendicular distance between the pivot point and the line of action of the force. In this case, the force of 5N is acting on the rod at point Y. To find the moment of this force about point X, we need to find the perpendicular distance between point X and the line of action of the force. From the diagram, we can see that the perpendicular distance between point X and the line of action of the force is 2m (the length of the rod). So, the moment of the force about point X is: Moment = force x perpendicular distance = 5N x 2m = 10Nm Therefore, the correct answer is: 10Nm.

In the diagram shown, which of the simple pendulum will resonate with P when set into oscillation?

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The product of force and time is?

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The product of force and time is known as impulse. Impulse can be defined as the change in momentum that an object experiences as a result of a force being applied to it over a period of time. In simpler terms, impulse is the "push" that an object receives from a force acting on it for a certain amount of time. The more force applied, or the longer the time the force is applied, the greater the impulse and the greater the change in momentum of the object. It's important to note that impulse is a vector quantity, meaning it has both magnitude and direction. Impulse is a measure of the ability of a force to cause an object to change its velocity, and can be used to explain many phenomena in physics, such as why a heavy object is harder to stop than a lighter one, or why a soccer ball changes direction when it is kicked.

The photo cell works on the principle of the

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The photocell works on the principle of the emission of electrons by incident radiation. In simple terms, a photocell is a device that converts light energy into electrical energy. It does this by using a material (such as silicon) that releases electrons when it is exposed to light. These electrons can then be collected and used to produce a current, which can be used to power an electrical device. The more light that hits the photocell, the more electrons are released and the greater the electrical current.

Which of the following phenomena cannot be explained by the molecular theory of matter?

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Conduction: the flow of internal energy from a region of higher temperature to lower temperature
Convection: heat transfer due to bulk movement of molecules within fluids
Expansion: the action of becoming larger or more extensive

An electric heating coil rated at 1KW is used to heat 2kg of water for 2 minutes. The initial water temperature is 30${}^o$C. Taking the specific heat of the water as 4,000Jkg ${}^{-1}$ and neglecting that of the container, the final water temperature is

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To determine the final temperature of the water, we can use the formula: Q = mcΔT where Q is the heat transferred, m is the mass of the water, c is the specific heat capacity of water, and ΔT is the change in temperature. We know that the power of the electric heating coil is 1KW, which means it transfers 1000 Joules of energy per second. In 2 minutes, or 120 seconds, it transfers 120,000 Joules of energy to the water. The mass of the water is given as 2kg and the specific heat capacity of water is 4000 J/kg°C. We can assume that the initial temperature of the water is 30°C. Using the formula, we can solve for the change in temperature: 120,000 J = (2 kg)(4000 J/kg°C)(ΔT) ΔT = 15°C Therefore, the final temperature of the water is 30°C + 15°C = 45°C. So, the final water temperature is 45.0oC.

Calculate the effective capacitance of the circuit in the diagram given

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The three 2uf capacitors are in parallel to each other so u add them like this
2uf+2uf+2uf=6uf
So u have three capacitors in series
6uf 2uf and 3uf
They are in series so
1/C= 1/6+1/3=1/2
C=2uf
Then the same thing with the last two capay
1/2+1/2=1uf
Thanks

The force between the molecules of a liquid in contact with that of a solid is?

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(ii) Adhesion : The force of attraction between unlike molecules, i.e. between the molecules of different liquids or between the molecules of a liquid and those of a solid body when they are in contact with each other, is known as the force of adhesion. This force enables two different liquids to adhere to each other or a liquid to adhere to a solid body or surface.

The critical angle for light travelling from a transparent medium to air s measured as 340. The refractive index of the medium is

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The critical angle is the angle of incidence at which light is just able to pass through the interface between two media and not reflect back. When light travels from a medium with a higher refractive index to a medium with a lower refractive index, it slows down and bends towards the normal. If the angle of incidence is increased, the light will eventually reach a point where it will not be able to escape the higher index medium and will be totally reflected back. This is the critical angle. The formula for the critical angle can be expressed as follows: sin(θc) = n2/n1 Where θc is the critical angle, n1 is the refractive index of the first medium, and n2 is the refractive index of the second medium. In this case, the first medium is the transparent medium and the second medium is air, which has a refractive index of approximately 1. By substituting the value of sin(θc) with the value of 340, and n2 with 1, we can solve for n1. sin(340) = n1/1 n1 = 1/sin(340) The value of n1 calculated using this formula is approximately 1.79, which means that the refractive index of the transparent medium is 1.79.

To keep a vehicle moving at a constant speed V requires power P from the engine. The force provided by the engine is

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The force provided by the engine to keep a vehicle moving at a constant speed is proportional to the power (P) required from the engine. This power is proportional to the product of the speed (V) and force (P), so the relationship can be expressed as P = kV, where k is a proportionality constant.

A ball of mass 800g moving horizontally with a speed of 5m/s hits a vertical wall and rebounds with the same speed. The impulse experienced by the ball is?

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The impulse experienced by the ball can be calculated using the principle of conservation of momentum, which states that the total momentum before the collision is equal to the total momentum after the collision. In this case, the momentum of the ball before the collision is: p1 = m * v1 where m is the mass of the ball and v1 is its velocity before the collision. Substituting the values given in the problem, we get: p1 = 0.8 kg * 5 m/s = 4 kg m/s After the collision, the ball rebounds with the same speed but in the opposite direction, so its velocity after the collision is: v2 = -5 m/s The momentum of the ball after the collision is: p2 = m * v2 Substituting the values, we get: p2 = 0.8 kg * (-5 m/s) = -4 kg m/s The negative sign indicates that the direction of the momentum is opposite to that before the collision. The change in momentum of the ball is given by: Δp = p2 - p1 Substituting the values, we get: Δp = (-4 kg m/s) - (4 kg m/s) = -8 kg m/s The negative sign indicates that the impulse experienced by the ball is in the opposite direction to its initial momentum, which is the direction of the wall. Therefore, the impulse experienced by the ball is 8 kg m/s. Therefore, the correct option is: 8kgm/s.

In homes, electrical appliances and lamps are connected in parallel because

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A resistor connected to a 12V battery draws a current of 2A. The energy dispatched in the resistor in 5 minutes is ___.

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To calculate the energy dispatched in the resistor, we need to use the formula: Energy = Power x Time Where Power is the amount of electrical power consumed by the resistor, and is equal to the product of the voltage across the resistor and the current flowing through it: Power = Voltage x Current In this case, the voltage across the resistor is 12V, and the current flowing through it is 2A. Therefore, the power consumed by the resistor is: Power = 12V x 2A = 24W Now, we can substitute this value of power along with the given time of 5 minutes into the formula for energy: Energy = 24W x 5min x 60s/min = 7,200J Therefore, the energy dispatched in the resistor in 5 minutes is 7,200J. is the correct answer.

A solid cube of side 50cm and mass 75kg floats in a liquid with $\frac{1}{3}$ of its height above the liquid surface. The relative density of the liquid is?

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Volume of liquid displaced
= $\frac{2}{3}$(0.5)${}^3$
Mass of liquid displaced = mass of floating cube = 75kg
Density of liquid = $\frac{mass}{volume}$
= $\frac{75}{\left(\frac{7}{3\left(0.5\right)}\right)}$ × 3
= 0.9 × 103kgm${}^{-3}$
R.D of liquid = $\frac{\left(0.9\right)}{\left(1.0\right)}$ × 103
= 0.9

Which of the following may be used to explain a mirage?

I. Layers of air near the road surface have varying refractive indices in hot weather

II. Road surfaces sometimes become good reflectors in hot weather

III. Light from the sky can be reflected upwards after coming close to the road surface.

Maelezo ya Majibu

The phenomenon of a mirage can be explained by options I and III. A mirage is an optical illusion that occurs when light rays passing through a medium with varying refractive indices create a false image of distant objects or even the sky. In hot weather, the air near the road surface becomes hotter and less dense than the air above, causing the light passing through it to bend and create a reflection of the sky or objects in the distance. This effect is known as a temperature inversion. Additionally, light from the sky can be reflected upwards after coming close to the road surface, adding to the illusion of a reflected object or the sky. Option II, which suggests that road surfaces become good reflectors in hot weather, is not a valid explanation for a mirage. Therefore, the correct answer is: I and III only.

Which of the following concepts is not an evidence of the particles nature of matter?

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The particle nature of matter refers to the idea that matter is made up of tiny particles that are constantly moving. Diffusion, Brownian motion, and crystallization are all examples of phenomena that can be explained by the particle nature of matter. However, diffraction is not an evidence of the particle nature of matter. Diffraction is a phenomenon that occurs when waves encounter an obstacle or a slit, causing them to spread out and interfere with each other. While particles can also exhibit diffraction, this is a property of waves and is not specific to particles. In summary, diffusion, Brownian motion, and crystallization are all evidences of the particle nature of matter, but diffraction is not.

The differences observed in solids, liquids and gases may be accounted for by

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The differences observed in solids, liquids, and gases can be accounted for by the spacing and forces acting between the molecules. In a solid, the molecules are packed closely together, so they have a fixed shape and volume. The intermolecular forces are strong enough to keep the molecules in a fixed position relative to one another. In a liquid, the molecules are still close together, but they are free to move around each other. The intermolecular forces are weaker than in a solid, so the molecules can slide past one another, giving the liquid its ability to flow and take the shape of its container. In a gas, the molecules are widely spaced and are in constant motion. The intermolecular forces are very weak, so the molecules are free to move around and fill any available space. Gases have no fixed shape or volume. So, the differences observed in solids, liquids, and gases can be explained by the spacing and forces acting between the molecules. It's not about their relative masses, melting points, or the different molecules in each of them.

Electrical power is transmitted at a high voltage rather than a low voltage because the amount of energy loss is due to

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The primary reason that power is transmitted at high voltages is to increase efficiency. As electricity is transmitted over long distances, there are inherent energy losses along the way. High voltage transmission minimizes the amount of power lost as electricity flows from one location to the next. How? The higher the voltage, the lower the current. The lower the current, the lower the resistance losses in the conductors. And when resistance losses are low, energy losses are low also. Electrical engineers consider factors such as the power being transmitted and the distance required for transmission when determining the optimal transmission voltage

The amount of heat needed to raise the temperature of 10kg of Copper by 1K is its

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The correct answer is "specific heat capacity." Specific heat capacity is a measure of how much heat energy is required to raise the temperature of a certain amount of a substance by 1 degree Celsius (or 1 Kelvin, which is the same size as 1 degree Celsius). In this case, we are dealing with 10kg of copper, so we need to know the specific heat capacity of copper. The specific heat capacity of copper is 0.385 J/g°C (joules per gram per degree Celsius). To calculate the amount of heat needed to raise the temperature of 10kg of copper by 1K, we need to know the total mass of copper (10kg) and the specific heat capacity of copper (0.385 J/g°C). The formula for calculating the amount of heat energy required is: Heat energy = mass x specific heat capacity x change in temperature Since we want to raise the temperature by 1K, the change in temperature is 1K. So, the amount of heat energy required to raise the temperature of 10kg of copper by 1K is: Heat energy = 10kg x 0.385 J/g°C x 1K = 3.85 kJ Therefore, it takes 3.85 kilojoules (kJ) of heat energy to raise the temperature of 10kg of copper by 1K.

Convex mirrors are used as driving mirrors because images formed are

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Convex mirrors are used as driving mirrors because the images formed by them are "erect, virtual, and diminished." Let me explain what these terms mean: - Erect: It means that the image appears upright, just like the actual object. This is important for a driving mirror because it allows the driver to perceive the correct orientation of the vehicles behind them. - Virtual: It means that the image appears to be behind the mirror, and not in front of it. This is also important for a driving mirror because it allows the driver to see a wider field of view without having to turn their head. - Diminished: It means that the image is smaller than the actual object. This is important for a driving mirror because it allows the driver to see a larger area behind them while still fitting it within the mirror's frame. Overall, these properties make convex mirrors ideal for use as driving mirrors as they provide the driver with an accurate view of the vehicles behind them without sacrificing their field of view.

The pitch of an acoustic device can be increased by

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The pitch of an acoustic device refers to the perceived highness or lowness of a sound, and is determined by the frequency of the sound wave. To increase the pitch of an acoustic device, you need to increase the frequency of the sound wave. This can be done by increasing the number of vibrations per second that the device produces. So, the correct answer is to "increase the frequency".

What effort will a machine of efficiency 90% apply to a load of 180N if its efforts arm is twice as long as its load arm?

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A narrow beam of white light can be split up into different colours by a glass prism. The correct explanation is that

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The correct explanation for why a narrow beam of white light can be split up into different colors by a glass prism is that different colors of white light travel with different speeds in glass. White light is made up of different colors with different wavelengths, ranging from violet to red. When a narrow beam of white light passes through a glass prism, the different colors refract at slightly different angles due to the fact that their wavelengths are different. This causes the different colors to spread out and form a spectrum. The amount of refraction that occurs depends on the speed of light in the medium. Different colors of light have different speeds in glass due to the fact that their wavelengths are different. This means that they will refract at different angles as they pass through the glass prism, causing them to spread out. So, the correct explanation for why a narrow beam of white light can be split up into different colors by a glass prism is that different colors of white light travel with different speeds in glass. Therefore, is the correct explanation. is incorrect because it describes what white light is made up of, but does not explain how it is split up into colors by a prism. is incorrect because a prism does not have all the colors of white light, but rather it separates the colors that are already present in white light. is incorrect because total internal reflection occurs when light is completely reflected back into the same medium, which is not what happens when white light is split up by a prism.

Shadows and eclipses result from the

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The rectilinear propagation of light means that light travels in straight lines as a wave. This can be observed in the well-defined shadows formed when an object blocks a light source and through the use of a pinhole camera.
According to Sudipa Sarkar, the formation of shadows with sharp edges demonstrates the rectilinear propagation of light, i.e. The fact that light travels in straight line. When an opaque obstacle is placed between a source of light and a screen, a shadow of the obstacle is formed on the screen. The kind of shadow depends on the size of the source of light. If it is a point source (light from a small hole), the shadow obtained is a region of total darkness, called umbra.
If an extended source of light, e.g. a bulb, is used, the umbra is surrounded by a region of partial darkness, called penumbra. The moon is seen because it reflects the sun's light. An eclipse of the moon (lunar eclipse) occurs when the earth comes between the sun and the moon and prevents some of the light from the sun from reaching the moon. In other words, the earth casts its shadow on the moon. The solar eclipse occurs when the moon comes between the sun and the earth.

An object weighs 30N in air and 21N in water. The weight of the object when completely immersed in a liquid of relative density 1.4 is

Maelezo ya Majibu

Weight of water displaced = upthrust = 30 - 21 = 9N
Mass of water displaced = $\frac{9}{10}$ = 0.9kg
Volume of object = 9 × 10${}^{-4}$m${}^3$
= (9 × 10${}^{-4}$) (1.4 ×103)

 = 1.26kg = 12N
30 - 12.6 = 17.4N