Question

A boy of mass 50 kg sits in a swing suspended by a rope 5 m long. A person p the swing to one side so that the rope makes an angle of 30° with the vertical. V is the gain in gravitational P.E. of the boy?​

Answer 1

Answer:

Explanation:

Let the swing be AC and the boy is at C. He is displaced to point D such that it makes angle 30 degree with the vertical.

Gravitational force is a conservative force i.e work done does not depend upon the path followed.

So to find gain in gravitational potential energy of the boy we need to find height 'h' to which he is displaced.

From triangle ABD we have,

cos30 = x/5

√3/2 = x/5

x=5√3/2

h=5–5√3/2=(10–5√3)/2=0.67m

Hence gain in gravitational potential energy

= mgh = 50×10×0.67=335 Joules.