Question

Kinetic energy of a body is directly proportional to its:
(A) Weight
(B) Speed
(C) Mass
(D) None

Answer 1

Hint : To answer this problem we first have to understand the meaning of the term kinetic energy. Kinetic energy is an energy an object that is possessed by the object due to its motion. It is generally the energy of mass in the motion. It is a scalar quantity hence does not require direction.

Complete step by step answer
As we have discussed kinetic energy is the energy possessed by an object when it is in motion. When a body is at rest it consists of certain energy which is known as potential energy. When that body comes into motion that stored energy also starts to convert into kinetic energy. The formula of kinetic energy is given by
$ \Rightarrow K.E = \dfrac{1}{2}m{v^2}$
Where $m$= mass and $v$= velocity.
Now from the above formula, we can see that kinetic energy is directly proportional to the mass $m$of the object and also to the squares of the velocity $v$ of the object.
$ \Rightarrow K.E \propto m$
Hence option (C) is the correct answer.

Additional Information
A very important aspect of kinetic energy is the ability to do work. Kinetic energy and work are interrelated. We can define the work as a product of force and distance hence $W = F.d$ and kinetic energy can be given by the formula $\dfrac{1}{2}m{v^2}$. Kinetic energy and work can be interchangeable also hence if we want to change the kinetic energy of a body then we have to do some work on it.

Note
Here we have to note that kinetic energy must be positive with any reference because we always take the square of the velocity and mass cannot be in the negative. So we have to consider that kinetic energy is always positive for any object that consists of mass and is in motion.