A ball is projected upwards from a point 4m above the ground with a speed of 4m/s. Find:(a) The speed of the ball when it is 15m above its point of...

The ball is projected upwards with a speed of 4 m/s from a
point 4 m above the ground. There is an acceleration on the ball due to the
gravitational force of attraction of the Earth equal to 9.8 m/s^2 acting
downwards.

Let the speed of the ball when it is 15 m above
its point of projection be v.

Use the formula v^2 - u^2 =
2*a*s, where v is the final velocity, u is the initial velocity, a is the acceleration
and s is the distance traveled.

v^2 - 4^2 =
2*15*(-9.8)

=> v^2 =
-278

This is not possible. We can infer that the ball
cannot reach a height of 15 m if it is projected at 4
m/s.

The maximum height that the ball can reach is 16/2*9.8
= 0.816 m.

The velocity of the ball when it hits the ground
is:

v^2 - 16 =
2*4*9.8

=> v = 9.715
m/s

=> v = 8.85 m/s