Name the physical quantity which causes motion in a body.
A. Force
B. Work
C. Energy
D. Power

Hint: In order to study the motion in the body, we need to study Newton’s first law which states that every object will remain at rest or in uniform motion in a straight line unless compelled to change its state by the action of an external force.

Complete step by step answer:
The three laws of Newton are fundamental in understanding the nature of motion in a body. Newton’s laws deal with the concept of “what caused the motion”.
The first law of Newton says that – every object will remain at rest or in uniform motion in a straight line unless compelled to change its state by the action of an external force.
The second law of Newton says that – the force applied on a body is equal to the mass time the acceleration in the body.
Force $F = ma$
From these two laws of motion, it is clear that the first law is one of the cases of the second law. The second law states that when the body is in motion it means that it has started from rest. So, to start from rest, where the velocity is zero to a finite velocity when it is in motion, we can clearly, say that there is an acceleration in effect starting from the rest to make a body move.
And thus, if the acceleration is finite, we can say that it is the FORCE applied to the body that has caused the movement in the body.

Hence, the correct option is Option A.

Note:
In the second law of motion equation; $F = ma$
If we substitute $a = 0$, we get $F = 0$
This is nothing but the mathematical form of the first law of motion which states that a body does not change its form of rest or motion (i.e. acceleration is 0) unless there is a force acting on the body.