Question

A metre rod of mass 1.2 kg is pivoted at one end and hangs vertically. It is displaced through an angle of 60. The increase in potential energy is (Given : g = 10 ms-2)

• A. 1 Joule
• B. 1.5 Joule
• C. 3 Joule
• D. 6 Joule

Answer 1

Answer: (C)

3 Joule

The mass of the rod is distributed all over its length.
In such a situation, the entire mass can be considered to be concentrated at Its centre of gravity , which in this case is at mid point of the rod.
As we can see from the figure the displacement in C.G is $1/4$ m
Therefore increase in its potential energy is given by,
$P=m\ast g\ast \left(1/4\right))=3J$