Question

A body of mass $m$ kg is rotating in a vertical circle at the end of a string of length $r$ metre. The difference in the K.E at the top and bottom of the circle is -

• A. $mgr$
• B. $2mgr$
• C. $\frac{mg}{r}$
• D. $\frac{2mg}{r}$

Answer 1

The correct option is B $2mgr$

The difference in kinetic energy arises to the height, as the particle reaches to highest point of the circle its one part of kinetic energy changes to potienal energy.

P. E. = mgh

P. E. = mg (2r)

Thererefore change in kinetic enegy is equal to increase in potential energy that is 2mgr.