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JAMB Physics Past Questions & Answers - Page 280

1,396.

A wheel and axle have radii 80cm and 10cm respectively. If the efficiency of the machine is 0.85, an applied force of 1200N to the wheel will raise a load of

8.0N

6.8N

8160N

9600N

View answer & explanation

Correct answer is C

Efficiency = m.A x $\frac{1}{V.R}$ x 100%

85 = $\frac{load}{1200}$ x $\frac{10}{80}$ x $\frac{100}{1}$

load = 8160N

1,397.

A spring of force constant 1500Nm^-1 is acted upon by a constant force of 75N. Calculate the potential energy stored in the string

1.9J

2.8J

3.45J

0.43J

View answer & explanation

Correct answer is A

P.E = $\frac{1}{2}$ Fe

= $\frac{1}{2}$ $\frac{F}{K}$

= $\frac{1}{2}$ x $\frac{75 \times 75}{1500}$

= 1.9J

1,398.

A body of mass 100g moving with a velocity of 10.0ms-1 collides with a wall. If after collision, it moves with a velocity of 2.0ms-1 in the opposite direction, calculate the change in momentum.

0.8Ns

1.2Ns

12.0Ns

80.0Ns

View answer & explanation

Correct answer is B

Initial momentum = 0.1 x 10 = 1Ns

final velocity = -2ms-1

Final momentum = -2 x 0.1 = -0.2Ns

Change in momentum = -0.2 - 1 = -1.2Ns

1,399.

An object moves with uniform speed round a circle. Its acceleration has

constant magnitude and constant direction

constant magnitude and varying direction

varying magnitude but constant direction

varying magnitude and varying direction

View answer & explanation

Correct answer is B

No explanation has been provided for this answer.

1,400.

A small metal ball thrown vertically upwards from the top of a tower with an initial velocity of 20ms^-1. If the ball took a total of 6s to reach ground level, determine the height of the tower [g = 10ms^-2]

60m

80m

100m

120m

View answer & explanation

Correct answer is A

Time from tower to top, t = $\frac{u - v}{g}$

= $\frac{20 - 0}{10}$

= 2s

distance from tower to top

x = ut - $\frac{1}{2}$ gt²

= (20 x 2) - ( $\frac{1}{2}$ x 10 x 2 x 2)

= 20m

Time from the top to the ground, t = 6 - 2

= 4s

distance from top to ground,

x = ut - $\frac{1}{2}$ gt²

= (0 x 4) + ( $\frac{1}{2}$ x 10 x 4 x 4)

= 80cm

therefore, height of tower = 80 - 20

= 60m