Velocity and Time of Ball Dropped from 20m Height

Question:

A ball is gently dropped from a height of 20 m. If its velocity increases uniformly at the rate of 10 ms^-2 . With what velocity will it strikes the ground?.After what time will it strike the ground?

Solution:

(i) With what velocity will it strike the ground?

Initial velocity of the ball u = o (Since the ball is at rest)

Acceleration due to gravity a= -g = 10 ms^-2

Velocity just before hitting the ground v=?

$${v^2 = \sqrt{2gh}}$$

$${v^2 =\sqrt {(2)(10)(20)}}$$

$${v= 20\frac {m} {s}} $$

Hence the ball will strike the ground at a velocity 20 ms^-1

(ii) After what time will it strike the ground?

Time taken by the ball is given by $$v=gt$$

$${t=\frac{v}{g}}$$

$${t=\frac {20} {10}}$$

$$t=2 s$$

Hence the ball will strike the ground at a velocity 20 ms^-1 at the time 2 s.