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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

- greatest speed.
- smallest speed.
- greatest acceleration?

Explain

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#### Solution

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.)

- At point B, it will gain the same speed as u and after that speed increases and will be maximum just before reaching C.
- 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.
- Acceleration is always constant throughout the journey and is vertically downward equal to g.

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