Question

A ball is thrown from a roof top at an angle of 45° above the horizontal. It hits the ground a few seconds later. At what point during its motion, does the ball have

1. greatest speed.
2. smallest speed.
3. greatest acceleration?

Explain

Answer 1

In this problem total mechanical energy of the ball is conserved. As the ball is projected from point O and covers the path OABC.

At point A it has both kinetic and potential energy.

But at point C it has only kinetic energy, (keeping the ground as a reference where PE is zero.)

1. At point B, it will gain the same speed as u and after that speed increases and will be maximum just before reaching C.
2. During the upward journey from O to A speed decreases and the smallest speed attained by it is at the highest point, i.e., at point A.
3. Acceleration is always constant throughout the journey and is vertically downward equal to g.