Question

How much should a spring of indefinite length be compressed to have a potential energy equivalent to a ball of mass 6 kg raised to a height of 120 m above the ground? Let the spring have a stiffness of k = 100 N/m and assume g = 10 m/s^2.

(a) 6m

(b) 12m

(c) 20m

(d) 144m

I have been asked this question in semester exam.

I want to ask this question from The Potential Energy of a Spring topic in chapter Work, Energy and Power of Physics – Class 11

Answer 1

Correct option is (b) 12m

To elaborate: PE of ball = m x g x h

 = 6 x 10 x 120

 = 7200 J

PE of spring = 1/2 x k x d^2

Given;

PE of ball = PE of spring

7200 = 1/2x k x d^2

 = 1/2 x 100 x d^2

d^2 = 144

d = 12 m.