Question

Which motion does not require force to maintain it?

• A. Uniform circular motion
• B. Elliptical motion
• C. Uniform straight line motion
• D. Projectile motion

Answer 1

Answer: (C)

In uniformly straight line motion there is no friction present.
According to Newtons second Jaw of motion $F=ma$
When body is moving uniformly along a straight line and there is no force of friction, acceleration/retardation of the body $a=0$.
$\therefore F=ma=0$
i.e., no external force is required.
For accelerated motion, force is necessary. In uniform circular motion, elliptical motion and projectile motion direction of velocity changes due to which force is imposed.