Question

9.
A ball is dropped from 100 m and it rebounds to a
height of 70 m. The percentage loss of energy is
[NCERT Pg. 125]
(1) 30%
(2) 70%
(3) 60%
(4) 10%​

Answer 1

Given :

• H = 100 m
• H' = 70m
• Acceleration due to gravity = 10 m / s

To find :

• Percentage loss of energy

Solution:

Initially, the ball is dropped from a height of 100 m .

The work done by the ball is equal to it's potential energy .

Hence ,

⇒ W = mgH

⇒ W = 100mg

Now the ball rebounds to a height of 70 m

Hence ,

⇒ W'= mg H'

⇒ W' = 70 mg

% Loss in energy

= ( W - W' / W )x 100

= ( 100mg - 70mg / 100 mg )x 100

= 30 %

Hence ,

Percentage loss in energy is 30 %.

Answer 2

Answer:

30%

Explanation:

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