Question

A metre stick of mass 400 gm is pivoted at one end and displaced through an angle 60ŗ. The increase in its potential energy is:

• A. 2 J
• B. 3 J
• C. 0 J
• D. 1 J

Answer 1

Answer: (D)

1 J

Answer 2

Centre of mass of a stick lies at the midpoint and when the stick is displaced through an angle 60ŗ it rises upto height 'h' from the initial position.

From the figure $h = \frac { l } { 2 } - \frac { l } { 2 } \cos \theta$ $= \frac { l } { 2 } ( 1 - \cos \theta )$

Hence the increment in potential energy of the stick

= mgh

$= m g \frac { l } { 2 } ( 1 - \cos \theta )$