JAMB UTME - Physics - 1987

A jet engine develops a thrust of 270Ns when the velocity of the exhaust gases relative to the engine is 300ms-1. What is the mass of the material ejected per second?

Detalhes da Resposta

Thrust = force x time

thrust = $\frac{m(v-u)}{t}$ x $\frac{t}{1}$

270 = m(300 - 0)

m = 0.90kg

The fig above shows two connected bodies of masses M1 and M2 in equilibrium under gravity. The tension in the upper string is

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A boat at anchor is rocked by waves whose crest are 100m apart and whose velocity is 25ms-1. At what interval does the wave crest reach the boat?

Detalhes da Resposta

Distance between the boat and crest = 100m

time = $\frac{100}{25}$

= 4sec

A body rolls down a slope from a height of 100m. its velocity at the foot of the slope is 20ms-1. What percentage of its initial potential energy is converted into kinetic energy? [g = 10ms-1]

Detalhes da Resposta

P.E = mgh = 1000m joules

K.E = $\frac{1}{2}$mv2 = 200m joules

%converted = $\frac{200m}{1000m}$ x 100

= 20%

he lowest note emitted by a stretched string has a frequency of 40Hz. How many overtones are there between 40Hz and 150Hz?

Detalhes da Resposta

In stretched strings the overtones are in odd multiple of Fo.

F1 = 3Fo

= 3 x 40 = 120Hz

F2 = 5Fo

= 5 x 40

= 200Hz

The distance between the fixed points of a centigrade thermometer is 20cm. What is the temperature when the mercury level is 4.5cm above the lower mark?

Detalhes da Resposta

20cm .... 100oC

4.5cm .... $\theta$

0cm ....0oC

$\frac{4.5-0}{20-0}$ = $\frac{0-0}{100-0}$

$\theta$ = 22.5oC

Two capacitance of 6$\mu$F and 8$\mu$F are connected in series. What additional capacitance must be connected in series with this combination to give a total of 3$\mu$F

Detalhes da Resposta

3 = $\frac{6\times 8\times c}{(6\times 8)+(6\times c)+(8\times c}$

therefore, C = 24$\mu$F

A galvanometer of resistance 20$\Omega$ is to be provided with a shunt that $\frac{1}{10}$ of the whole current in a circuit passes through the galvanometer. The resistance of the shunt is

Detalhes da Resposta

$\frac{1}{10}$I x 20 = $\frac{9}{10}$I x Rs

Rs = 2.22$\Omega$

Isotopes are nuclei which have

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The length of a side of a metallic cube at 20oC is 5.0cm. Given that the linear expansivity of the metal is 4.0 x 10-5k-1, find the volume of the cube at 120oC .

Detalhes da Resposta

Y = $\frac{V_2-V_1}{V_1\times \theta }$

3 x 4 x 10-5 = $\frac{V_2-125}{125\times (120-20)}$

V2 = 126.50cm3

When the length I of a piece of wire under constant tension is varied, the relationship of the frequency of the vibration f$\alpha$/ is

Detalhes da Resposta

F = $\frac{1}{2L}\sqrt{\frac{T}{m}}$

A wave has a frequency of 2Hz and a wavelength of 30cm. The velocity of the wave is

Detalhes da Resposta

V = F$\lambda$

= 2 x 0.3

= 0.6ms-1

Which of the following instruments has a pure tone?

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A ray of light is incident at an angle of 30o on one top surface of a parallel-sided glass block of refractive index 1.5. The ray finally emerges from the lower surface. What is the angular deviation of the emergent ray?

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The direction of the magnetic field at a point in the vicinity of a bar magnet is

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A man walks 8km north and then 5km in a direction 60o east of north. Find the distance from his starting point

Detalhes da Resposta

R = $\sqrt{5^2+8^2-2\times 5\times 8\times cos{120}^o}$

R = $\sqrt{129}$

= 11.36km

In which of the following are the substance arranged in descending order of their thermal conductivities?

Detalhes da Resposta

Which of the following units is equivalent to kgms-1?

Detalhes da Resposta

kgms-1 = $\frac{mass}{distance}$

since, F = ma = kgms-1 = N

kgms-1 = Ns

The fig above represents the main sequence of energy conversion at Kainji dam. What is the efficiency of the system?

Detalhes da Resposta

A pool of water appears to be 1.0m deep when viewed vertically from above. If the refractive index of water is 1.33, what is the actual depth of the pool?

Detalhes da Resposta

n = $\frac{\text{real depth}}{\text{apparent depth}}$

1.33 = $\frac{\text{real depth}}{1}$

real depth = 1.33cm

A radioactive sample initially contains N atoms. After three half-lives the number of atoms that have disintegrated is

Detalhes da Resposta

N $\to$ $\frac{N}{2}$ $\to$ $\frac{N}{4}$ $\to$ $\frac{N}{8}$

In the figure above, M and N are insulated metal spheres in contact. A negatively charged ebonite rod P is I brought near M. When M and N are Separated and the rod is taken away, which of the following statements is correct

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The vacuum in a thermos flask helps to reduce heat transfer by?

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An elevator of mass 4800kg is supported by a cable which can safely withstand a maximum tension of 60 000N. The maximum upward acceleration the elevator can have is

Detalhes da Resposta

a = $\frac{F}{m}$

= $\frac{60000-(4800\times 10)}{4800}$

= 2.5ms-2

Which of the following statements is TRUE of photoelectric effect?

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When two parallel wires carry currents in opposite directions, the force on either wire is

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Which of the following phenomena explains the fact that a house whose roof is coated with white paint will be cooler in the hot season than one coated with black paint ?

Detalhes da Resposta

A load of 5N gives an extension of 0.56cm in a wire which obeys Hooke's law. What is the extension caused by a load of 20N?

Detalhes da Resposta

$\frac{F_1}{e_1}$ = $\frac{F_2}{e_2}$

$\frac{5}{0.56}$ = $\frac{20}{e_2}$

e2 = 2.24cm

If a beaker is filled with water it is observed that the surface of the water is not horizontal at the glass-water interface. This behavior is due to

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The velocity time graph above describes the motion of a particle between two points P and Q. What is the distance between P and Q?

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A 50kg block is dropped from a point 10cm above as shown in the fig above. if the force constant of the spring is 4.0 x 104Nm-1, find the maximum compression of the spring [g = 10ms-2]

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22,000J of heat is required to raise the temperature of 1.5kg of paraffin from 20oC to 30oC. Calculate the specific heat capacity of paraffin.

Detalhes da Resposta

22,000 = 1.5 x c x (30 - 20)

c = 1466Jkg-1oC-1

A constant force of 40N acting on a body initially at rest gives an acceleration of 0.1ms-2 for 4s. Calculate the work done by the force

Detalhes da Resposta

X = ut + $\frac{1}{2}$at2

= (0 x 4) + ($\frac{1}{2}$ x 0.1 x 4 x 4)

= 0.8m

workdone = force x distance

= 40 x 0.8

= 32J

he coefficient of static friction between a 40kg crate and concrete surface is 0.25. Find the magnitude of the minimum force needed to keep the crate stationary on the concrete base inclined at 45o to the horizontal. [G = 10ms-1]

Detalhes da Resposta

momentum force = R5n$\theta$ - $\mu$Rcos$\theta$

Fm = (40 x 10 x sin 45) - (40 x 10 x 0.25 x cos 45)

= 212N

Which of the following statements supports the assumption that light travels in straight lines?

Detalhes da Resposta

Hot water is added to three times its mass of water at 10oC and the resultant temperature is 20oC. What is the initial temperature of the hot water?

Detalhes da Resposta

Heat loss = heat gained

mh x ch x $\theta$h = mc x cc x $\theta$c

mh x ch x ($\theta$ - 20) = mc x cc x (20 - 10)

ch = cc ; mc = 3mh

therefore, $\theta$ = 50oC

When a transformer has more secondary windings than primary windings, it

Detalhes da Resposta

A current of 0.5A flows through a resistor when connected to a 40-V battery. How much energy is dissipated in 2 minutes?

Detalhes da Resposta

Electrical energy = IVT

= 0.5 x 40 x 2 x 60

= 2400J

Detalhes da Resposta

As a result of air at the top of a barometer, the height of the mercury column is 73.5cm when it should be 75.0cm; the volume of the space above the mercury is 8.0cm3. Calculate the correct barometer height when the barometer reads 74.0cm and the volume of the space above the mercury is 6.0cm3.

Detalhes da Resposta

Using, P1P1 = P2P2

(75 - 73.5) x 8 = (X - 74) x 6

X = 76cm

What type of reaction is represented by the following scheme? ${}_1^{2}X$ + ${}_1^{2}Y$ + ${}_2^{3}Z$ + ${}_0^{1}n$ + energy

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The mechanical advantage (MA) of an inclined plane depends on

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Four lenses are being considered for use as a microscope objective. Which of the following focal lengths is most suitable?

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If an object is placed in front of two mirrors inclined at 90o, how many images will be formed?

Detalhes da Resposta

n = $\frac{360}{\theta }$ - 1

= 360 - 1

= 3 images

In the above, a voltage V is applied across the terminals P and Q. The voltage across the 1 ohm resistor is

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A cube of side 10cm and mass 0.5kg floats in a liquid with only $\frac{1}{5}$ of its height above the liquid surface. What is the relative density of the liquid?

Detalhes da Resposta

Height below liquid = 1 - $\frac{1}{5}$ = $\frac{4}{5}$

volume of cube = 103cm3

volume of liquid displaced = $\frac{4}{5}$ x 1000

= 800cm3

density of liquid displaced;

= $\frac{500}{800}$

= 0.625cm-1

Calculate the amount of heat required to convert 2kg of ice at 2oC to water at 0oC. [specific heat capacity of ice = 2090Jkg-1oC-1, specific latent heat of fusion of ice = 333kJkg-1]

Detalhes da Resposta

Q = mL + mc$\theta$

= (2 x 333000) + (2 x 2090 x 2)

= 674 360J

An object 3.0cm high is placed 60.0cm from a converging lens whose focal length is 20.0cm. Calculate the size of the image formed

Detalhes da Resposta

F = $\frac{UV}{U+V}$

20 = $\frac{60\times V}{60+V}$

V = 30cm

similarly, $\frac{U}{V}$ = $\frac{\text{height of object}}{\text{height of image}}$

$\frac{60}{30}$ = $\frac{3}{h}$

h = 1.5cm