1998 - JAMB Physics Past Questions & Answers - page 1

1
A bullet fired at a wooden block of thickness 0.15m manages to penetrate the block. If the mass of the bullet is 0.025kg and the average resisting force of the wood is 7.5 x 103N, calculate the speed of the bullet just before it hits the wooden block.
A
450ms-1
B
400ms-1
C
300ms-1
D
250ms-1
CORRECT OPTION: c
F = ma

Therefore, a = $$\frac{F}{m}$$

a = $$\frac{7.5 \times 10^{3}}{0.025}$$

a = 3 x 105m/s2

using V2 = U2 + 2ax;

V2 = 02 + (2 x 3 x 105 x 0.15)

Therefore V = 300 m/s
2
The velocity of a sound wave at 27oC is 360ms-1. Its velocity at 127oC is
A
120√3 ms-1
B
240 ms-1
C
240√3 ms-1
D
720√3 ms-1
CORRECT OPTION: c
Velocity $$\alpha \sqrt{temperature}$$

$$\frac{V_1}{V_2} = \sqrt{\frac{T_1}{T_2}}$$

therefore, $$\frac{360}{V_2} = \sqrt{\frac{27 + 273}{127 + 273}}$$

$$V_2 = 240\sqrt{3}$$m/s
3
The physical quantity that has the same dimensions as impulse is
A
energy
B
momentum
C
surface tension
D
pressure
CORRECT OPTION: b
Impulse = F x t = m(v-u)
4
A ball is moving at 18ms-1 in a direction inclined at 60o to the horizontal. The horizontal component to its velocity is
A
9√3ms-1 ·
B
6√3ms-1 ·
C
8√3ms-1 ·
D
9ms-1 ·
CORRECT OPTION: d
5
In free fall, a body of mass 1kg drops from a height of 125m from rest in 5s. How long will it take another body of mass 2kg to fall from rest from the same height? [g = 10ms-1·]
A
5s
B
10s
C
12s
D
15s
CORRECT OPTION: a
In free fall, every object will reach the ground at same time
6
A ball of mass 0.15kg is kicked against a rigid vertical wall with a horizontal velocity of 50ms-1. If it rebounced with a horizontal velocity of 30ms-1, Calculate the impulse of the ball on the ball · ·
A
3.0Ns
B
4.5Ns
C
7.5Ns
D
12.0Ns
CORRECT OPTION: b
Impulse = m(v-u)

= 0.15(80-50)

= 4.5N/s
7
The force of attraction between two point masses is 10-4N when the distance between them is 0.18m. If the distance is reduced to 0.06m, calculate the force.
A
1.1 x 10-5N
B
3.3 x 10-5N
C
3.0 x 10-4N
D
9.0 x 10-4N
CORRECT OPTION: d
F $$\alpha \frac{1}{r^2}$$

therefore, $$\frac{F_1}{F_2}$$ = $$\frac{r_1}{(r_2)^2}$$

$$\frac{10^{-4}}{F_2}$$ = $$\frac{(0.06)^2}{(0.18)^2}$$

F = 9 x 10-4N
8
A uniform meter rule weighing 0.5N is to be pivoted on a knife-edge at the 30cm-mark. where will a force of 2N be placed from the pivot to balance the meter rule?
A
95cm
B
25cm
C
20cm
D
5cm
CORRECT OPTION: b
9
A man whose mass is 80kg climbs a staircase in 20s and expends power of 120W. Find the height of the staircase.[g = 10ms-2]
A
1.8m
B
2.0m
C
2.5m
D
3.0m
CORRECT OPTION: d
Power x time = mgh

120 x 20 = 80 x 10 x h

2400 = 800h

making h the subject of formula,divide both side by 800

$$\frac{2400}{800}$$ = h

h = 3m
10
A parachute attains a terminal velocity when
A
its density is equal to the density of air
B
the viscous force of the air and the upthrust completely counteract its weight
C
it expands as a result of reduced external pressure
D
the viscous force of the air is equal to the sum of the weight and upthrust
CORRECT OPTION: b
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