Question

A person applies a constant force $F$ on a particle of mass m and finds that the particle moves in a circle of radius $r$ with a uniform speed v when seen from an inertial frame of reference.

• A. This is not feasible
• B. Some other force whose resultant varies in magnitude and direction also act on the particle
• C. The resultant of other forces is $\frac{{mv}^2}{r}$ towards the center
• D. none of these

Answer 1

The correct option is B Some other force whose resultant varies in magnitude and direction also act on the particle

The person applies $F$ constantly in a fixed direction. So to keep the particle in constant circular motion of radius $r$ and uniform speed $v$, some other force whose resultant varies in magnitude and direction also act on the particle. Since the resultant of F and other force has to have constant magnitude but varying direction, the magnitude and direction of the other force has to change from point to point on circle.