Question

A body is said to be in dynamic equilibrium if:
A. When it is in uniform motion along a straight line
B. When it is moving with changing acceleration
C. When it is in uniform motion along a circular path
D. When it possesses instantaneous velocity

Answer 1

Hint:Recall the concept of dynamic equilibrium. This concept includes the conditions for velocity, acceleration and force on the body in motion.

Complete step by step answer:
An object is said to be in dynamic equilibrium if it is moving with a uniform linear velocity throughout its rectilinear motion or if it is moving with uniform angular velocity throughout its circular motion.Hence, for the object in dynamic equilibrium, the net force on the object and hence the net acceleration is zero.
-When the body is moving with the changing acceleration, its velocity is not uniform. Hence, the net force on the body is also not zero.Therefore, the body moving with changing acceleration is not in dynamic equilibrium.Hence, option B is incorrect.
-When the body is in uniform circular motion, the velocity of the body is continuously changing and is not uniform. Hence, the angular velocity of the body is also non-uniform.
Therefore, a body moving in uniform circular motion is not in dynamic equilibrium.Hence, the option C is incorrect.
-When a body possesses instantaneous velocity, its velocity is changing at every instant and hence, the velocity is not uniform.Therefore, a body possessing instantaneous velocity is not in dynamic equilibrium.Hence, the option D is incorrect.
-When a body is in uniform motion along a straight line, the velocity of the body is uniform. So, the net acceleration and hence the net force acting on the body is zero.
Therefore, a body is in uniform motion along a straight line and is in dynamic equilibrium.

Hence, the correct option is A.

Note:The body performing uniform circular motion may also be in dynamic equilibrium if we consider that the centripetal force is balanced by the centrifugal force. Since the centrifugal force is a pseudo force, one can neglect it to choose the most appropriate and obvious option.