# 1997 - WAEC Physics Past Questions and 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\(s^{-1}\)

**Answer & Comments**

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\(ms^{-2}\)

**Answer & Comments**

**correct option:**b

\(v^2=u^2 +2as =0 +2\times(25-5)\ v^2 =0+20\times 20=400;v =\sqrt{400}= 20(ms^{-2}\)

Users' Answers & Comments3

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

**Answer & Comments**

**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

Users' Answers & Comments4

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

**Answer & Comments**

**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

**Answer & Comments**

**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

**Answer & Comments**

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

**Answer & Comments**

**correct option:**a

Upthrust = Volume of fluid displaced =vpg =0.2 x 0.2 x 0.2 x0.8 x 10= 0.064N

Users' Answers & Comments8

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

**Answer & Comments**

**correct option:**e

H=\(mc\Delta\theta \Rightarrow 60=0.03\times400\times\Delta\theta\60= 12\Delta\theta therefore \Delta\theta=60/12 =5K\)

Users' Answers & Comments9

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\(10^{-1}cm\)

**Answer & Comments**

**correct option:**d

\(\alpha= \frac{\Delta{L}}{L_1\Delta\theta}; \Delta{L}=\alpha{L_1}\Delta\theta\Rightarrow 1.0\times 10^{-5}\times 3\times (40-28)= 3.6\times 10^{-2}\)

Users' Answers & Comments10

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

**Answer & Comments**

**correct option:**a