Question

A spool is pulled horizontally by two equal and opposite forces on a frictionless surface as shown in the figure. Which of the following statements are correct?

A. The centre of mass moves towards the left.
B. The centre of mass moves towards the right.
C. The centre of mass remains stationary.
D. The net torque about the centre of mass of the spool is zero.

Answer 1

Hint:Before we look into the question let’s understand the frictional force and torque. The frictional force is the opposing force created between the two surfaces that try to move in the same direction or that try to move in opposite directions. The frictional force is to create a resistance to the motion of one surface over the other. When a force is applied to a body, and the force causes a rotational motion in the body, that force is known as torque.

Complete step by step solution:

Image: A spool on a frictionless surface.

Consider a spool as shown in the figure. Now if we apply two equal and opposite forces on the spool, hence the net torque produced on the spool is zero. and the centre of mass of the spool remains stationary.

Since there is no external force acting on it (i.e., friction) the body starts spinning due to the applied force, and hence the centre of mass of the spool remains stationary. Therefore, the centre of mass of the spool remains stationary.

Hence, option C is the correct answer.

Note:The different types of motion of the object gives different types of friction. Basically, there are 4 types of friction : static friction, sliding friction, rolling friction, and fluid friction.