Question

A particle is acted upon by a force of constant magnitude which is always perpendicular to the velocity of the particle, the motion of the particle takes place in a plane. It follows that

• A. its velocity is constant
• B. its acceleration is constant
• C. its kinetic energy is constant
• D. it moves in a straight line.

Answer 1

Answer: (C)

its kinetic energy is constant

Answer 2

Since the particle is acted upon by a force of constant magnitude which is always perpendicular to the velocity of the particle, so work done by the force in the direction of the velocity is zero. So the magnitude of velocity will not change due to the force. Kinetic energy is $KE =\frac{1}{2} mv ^{2}=$ constant. Now mass and magnitude of velocity will always be constant in this given situation so the kinetic energy will also be constant.