Problem 1CQ

What can you say about the velocity of a moving body that is in dynamic equilibrium? Draw a sketch of such a body using clearly labeled arrows to represent all external forces on the body.

Solution 1CQ

When a body moves at a constant velocity, the net force and torque acting on it are zero, the body is said to be in dynamic equilibrium.

The sketch of a body in dynamic equilibrium is shown below.

Let us consider a block of mass being pushed from left by a force. The force is with drawn and it attains a constant velocity. This constant velocity will not be disturbed unless another force is applied from the right direction on the block. The only force acting on the block from the opposite direction is the force of friction which is very small in magnitude as compared to the applied force. So, it cannot have a significant impact on the velocity of the block.

The weight of the block is balanced by the normal reaction offered by the floor on which it is moving.

Therefore, the net force acting on the block is zero and it will continue to move with a constant velocity.