Chapter - 1 Motion

Q&A -Ask Doubts and Get Answers

Q
Motion

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?

Answer:

Distance covered by the ball, S = 20 m

Acceleration, a = 10 ms-2

Initial velocity, u = 0 (since the ball was initially at rest)

Let final velocity of the ball with which it strikes the ground is v.

According to the third equation of motion:

v^2=u^2+2as

v^2=(0)^2+2 	imes 10 	imes 20

v^2=400

v=sqrt{400}=20 m/s

v=20 m/s

According to the first equation of motion:

v=u+at

Where,

Time, t is taken by the ball to strike the ground is,

20=0+10 	imes t

t=2 s

Hence the ball strikes the ground after 2 s with a velocity of 20 m/s.


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