Question

A long spring is stretched by 2 cm, its potential energy is U. If the spring is stretched by 10 cm, the potential energy stored in it will be

• A. U / 25
• B. U / 5
• C. 5 U
• D. 25 U

Answer 1

Answer: (D)

25 U

Answer 2

Elastic potential energy of a spring $U = \frac { 1 } { 2 } k x ^ { 2 }$

∴$U \propto x ^ { 2 }$

So $\frac { U _ { 2 } } { U } = \left( \frac { 10 \mathrm {~cm} } { 2 \mathrm {~cm} } \right) ^ { 2 }$⇒ $U _ { 2 } = 25 U$