# 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? - Science

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?

#### 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)

= 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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Chapter 8: Motion - Exercises [Page 113]

#### APPEARS IN

NCERT Class 9 Science
Chapter 8 Motion
Exercises | Q 7 | Page 113
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