Question

A liquid flows through a tube of uniform cross-section with a constant speed in the direction as shown by the arrows in fig. The liquid exerts on the tube

A. a net force to the left
B. a net force to the right
C. an anticlockwise torque
D. a clockwise torque

Answer 1

Hint: It’s very convenient to solve this question by observing the above diagram. Also we should know how the momentum of the liquid changes from one end to other end of the tube which in turn forms the couple.

Complete step by step answer:
The forces exerted by the liquid at the bends are shown. The liquid undergoes change of momentum only at these points, and hence the liquid and tube exert forces on each other. The two forces form a couple exerting a clockwise torque.The force exerted by the liquid at the bends is shown. The liquid undergoes change in momentum at these points. The two force from a couple exerting a clockwise torque.

Hence the correct option is D.

Note: The couple force is the same as that of torque. It is the equivalent to the rotational force is the same as linear force. Usually torque is also referred to as moment of force or turning force. In the mechanics, force of linear is a push or a pull exerted on the body, whereas in rotational dynamics, a torque can be referred to as a twist to an object around a fixed axis.