Question

Question 6
a)
A stone at rest is dropped from a height of 15 m. It loses 30% of its kinetic
energy in striking the ground. Calculate the height to which it bounces back
from the ground.
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Answer 1

Answer:

10.5 m

Explanation:

New height=15•(100-30)/100

= 10.5 metres

Answer 2

The height to which the ball bounces back  from the ground is 10.5 m.

- The kinetic energy of the ball on reaching the ground will be equal to its initial potential energy.

⇒ K E = Initial P E

⇒ K E = m × g × h

⇒ K E = m × g × 15

- Since the ball loses 30 % of its K E, the remaining energy will be used to rise it to some height, i.e.,

1 - (30/100) × m × g × 15 = m × g × h

⇒ h = 0.7 × 15

⇒ h = 10.5 m