A ball is gently dropped from a height of 20 m. If its velocity increases uniformly at the rate of 10 m s-2, with what velocity will it strike the ground? After what time will it strike the ground?
Distance covered by the ball, s = 20 m
Acceleration, a = 10 m/s2
Initially, velocity, u = 0
Final velocity, v = ?
Time, t = ?
According to the third equation of motion:
v2 = u2 + 2 as
v2 = 0 + 2 (10) (20)
v = 20 m/s
According to the first equation of motion:
v = u + at
20 = 0 + 10 (t)
t = 2 s
Hence, time taken to reach at the ground is 2 seconds.
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Fig. 8.11
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(c) How far has C travelled when B passes A?
(d) How far has B travelled by the time it passes C?
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The speed-time graph for a car is shown is Fig. 8.12.
Fig. 8.12
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