Question

A ball falling from a height of 20 m hits a floor and bounces back to a height of 17 m. The percentage of energy lost by the ball during the impact is

• A. 7.5
• B. 10
• C. 15
• D. 5
• E. 20

Hint:

Percentage energy loss is directly proportional to the change in height: $\frac{\Delta h}{h_{initial}} \times 100$.

Answer 1

The Correct Option is C

Step 1: Concept
Gravitational potential energy ($U$) is given by $mgh$.

Step 2: Meaning
The energy lost is the difference between the initial potential energy at 20 m and the final potential energy at 17 m.

Step 3: Analysis
Initial energy $E_i = mg(20)$. Final energy $E_f = mg(17)$.
Percentage loss $= \frac{E_i - E_f}{E_i} \times 100 = \frac{20 - 17}{20} \times 100 = \frac{3}{20} \times 100 = 15\%$.

Step 4: Conclusion
Hence, the percentage of energy lost is 15.
Final Answer: (C)