Question

In which of the following cases forces may not be required?

• A. to keep the particle going in a circle.
• B. to keep the particle going along a straight line with variable acceleration.
• C. to keep the momentum of the particle constant
• D. to keep the acceleration of the particle constant.

Answer 1

The correct option is C to keep the momentum of the particle constant

We know that force is the rate of change of momentum,
$F=\frac{dp}{dt}$ where $p=$momentum

If the rate of change of momentum is zero or constant, net force acting on the body will be zero.

$F=\frac{dp}{dt}=0$ $p=$ Constant