Question

A body of mass m is moving in a circle of radius r with a constant speed v. The force on the body is $\frac { m v ^ { 2 } } { r }$ and is directed towards the centre. What is the work done by this force in moving the body over half the circumference of the circle

• A. $\frac { m v ^ { 2 } } { \pi r ^ { 2 } }$
• B. Zero
• C. $\frac { m v ^ { 2 } } { r ^ { 2 } }$
• D. $\frac { \pi r ^ { 2 } } { m v ^ { 2 } }$

Answer 1

Answer: (B)

Zero

Answer 2

Work done by centripetal force is always zero, because force and instantaneous displacement are always

perpendicular.

$W = \vec { F } \cdot \vec { s } = F s \cos \theta = F s \cos \left( 90 ^ { \circ } \right) = 0$