# 1997 - WAEC Physics Past Questions & Answers - page 1

1
An object of mass 0.40 kg attached to the end of a string is whirled around in a horizontal circle of radius 2.0m with a constant speed of 8$$ms^{-1}$$. Calculate the angular velocity of the object
A
0.8rad$$s^{-1}$$
B
2 rad$$s^{-1}$$
C
4 rad$$s^{-1}$$
D
8 rad$$s^{-1}$$
CORRECT OPTION: c
2
An object falls freely from a height of 25m onto the roof a building 5m high. Calculate the velocity with which the object strikes the roof (g=10$$ms^{-2}$$
A
17.3$$ms^{-2}$$
B
20$$ms^{-2}$$
C
24.5$$ms^{-2}$$
D
125$$ms^{-2}$$
CORRECT OPTION: b
$$v^2=u^2 +2as =0 +2\times(25-5)\ v^2 =0+20\times 20=400;v =\sqrt{400}= 20(ms^{-2}$$
3
A ball of mass 0.1kg approaching a tennis player with a velocity of 10$$ms^{-1}$$,is hit back in the opposite direction with a velocity of 15$$ms^{-1}$$. If the time of impact between the racket and the ball is 0.01s, calculate the magnitude of the force with which the ball is hit
A
5000N
B
500N
C
250N
D
50N
CORRECT OPTION: d
M =0.1kg; F=$$m\left(\frac{v-u}{t}\right) = 0.1\left(\frac{15-(-10)}{0.01}\right)$$ F=50N
4
Two blocks of the same dimension, one steel and the other wooden are dropped simultaneously from the same height. If they fall freely neglecting air resistance the
A
Two blocks hit the ground simultaneously because they have the same acceleration
B
Two blocks reach the ground at the same time because their dimensions are the same
C
Wooden block being lighter than the steel block reaches the ground first
D
Steel block reaches the ground first because it is denser than the wooden block
CORRECT OPTION: d
5
Two forces 3N and 4N act on a body in directions due north and due east respectively. Calculate their equilibrant
A
5N 53° east of North
B
5N 53° west of the south
C
5N 37° north of east
D
7N 37° west of North
CORRECT OPTION: c
6
A missile weighing 400N on the earth surface is shot into the atmosphere to an altitude of 6.4 x $$10^{-6}$$m. Taking the earth as a sphere of radius 6.4 x $$10^{-6}$$m and assuming the inverse-square law of universal gravitation, what would be the weight of the missile at that altitude?
A
100N
B
200N
C
400N
D
800N
CORRECT OPTION: a
W=$$\frac{mg}{4}= \frac{400}{4}=100N$$
7
A solid plastic cube of side 0.2m is submerged in a liquid density of 0.8kg$$m^{-3}$$. Calculate the upthrust of the liquid on the cube (g=10$$ms^{-2}$$
A
0.064N
B
0.025N
C
0.016N
D
0.008N
CORRECT OPTION: a
Upthrust = Volume of fluid displaced =vpg =0.2 x 0.2 x 0.2 x0.8 x 10= 0.064N
8
A piece of copper of mass 30g loses 60J of heat energy. If the specific heat capacity of copper is 400J$$kg^{-1}K^{-1}$$, Calculate the change in the temperature of the copper
A
0.2K
B
0.8K
C
2K
D
4.5K
CORRECT OPTION: e
H=$$mc\Delta\theta \Rightarrow 60=0.03\times400\times\Delta\theta\60= 12\Delta\theta therefore \Delta\theta=60/12 =5K$$
9
Steel bars each of length 3m at 28°C are to be used for constructing a rail line. If the linear expansitivity of the steel is 1 x $$10^{-5}K^{-1}$$,what is the safety gap that must be left between the successive bars if the highest temperature expected is 40°C?
A
1.2x $$10^{-1}cm$$
B
7.2x$$10^{-1}cm$$
C
6x$$10^{-1}cm$$
D
3.6x$$10^{-1}cm$$
CORRECT OPTION: d
$$\alpha= \frac{\Delta{L}}{L_1\Delta\theta}; \Delta{L}=\alpha{L_1}\Delta\theta\Rightarrow 1.0\times 10^{-5}\times 3\times (40-28)= 3.6\times 10^{-2}$$
10
Which of the following explains why a thick glass cup cracks when boiling water is poured into it?
A
Unequal expansion of the exterior and interior walls of the cup
B
Anomalous expansion of the water
C
Greater specific latent capacity of water compared with that of glass
D
Large increase in the heat capacity of the cup
CORRECT OPTION: a
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