1
Question
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?
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?
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Solution
Distance
covered by the ball, s
= 20 m
Acceleration,
a = 10
m/s2
Initially,
velocity, u
= 0 (since the ball was initially at rest)
Final
velocity of the ball with which it strikes the ground,
v
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
Where,
Time,
t taken by
the ball to strike the ground is,
20 =
0 + 10 (t)
t
= 2 s
Hence,
the ball strikes the ground after 2 s with
a velocity of 20 m/s.
Distance covered by the ball, s = 20 m
Acceleration, a = 10 m/s2
Initially, velocity, u = 0 (since the ball was initially at rest)
Final velocity of the ball with which it strikes the ground, v
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
Where,
Time, t taken by the ball to strike the ground is,
20 = 0 + 10 (t)
t = 2 s
Hence, the ball strikes the ground after 2 s with a velocity of 20 m/s.
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