Kinetic Energy

The motion of an object has the energy that constitutes the Kinetic energy.

What is Kinetic Energy?

A force must be applied on a body to accelerate an object. Work must be done in order to apply a force. The body will move with an unvarying speed after the work has been done due to the energy provided by it. The speed and the mass of the body are factors on which the energy transfer that makes up the kinetic energy depends.

Just like all forms of energy, Kinetic energy too can be transformed into other forms of energy and transmitted amongst objects. For instance, a moving car may hit a stationary person and then the kinetic energy of the car gets transferred into the person’s body.

How to Calculate Kinetic Energy?

To simply put, Kinetic energy can be calculated by the basic process of computing the work (W) that is done by a force (F). If the body has a mass of m that was pushed for a distance of d on a surface with a force that’s parallel to it.

\(W=F.d=m.a.d\)

The acceleration in this equation can be substituted by the initial (vi) and final (vf) velocity and the distance. This we get from the kinematic equations of motion.

\(W=m.a.d\\ \\ =m.d.\frac{v_{f}^{2}-v_{i}^{2}}{2d}\\ \\ =m.\frac{v_{f}^{2}-v_{i}^{2}}{2d}\\ \\ =\frac{1}{2}.m.v_{f}^{2}-\frac{1}{2}.m.v_{i}^{2}\)

The Kinetic Energy’s (K) basic quantity ½mv2 changes when a particular sum of work is acted upon an object.

\(K.E=\frac{1}{2}mv^{2}\)

The total work that is done on a system is equivalent to the change in kinetic energy. Thus,

\(W_{net}=\Delta K\)

This equation is known as the work-energy theorem and has large applications even if the forces applied varies in magnitude and direction. This factor is an important one in the concept of conservation of energy.

Examples of Kinetic Energy

  • A semi truck travelling down the road has more kinetic energy than a car travelling at the same speed because the truck’s mass is much more than the car’s.
  • A river flowing at a certain speed comprises kinetic energy as water has certain velocity and mass.

Kinetic Energy Facts – What’s Interesting?

The equation tells us some interesting things about kinetic energy:

  • The velocity of a body when squared is dependent on the kinetic energy. This tells us that when the velocity of a body is doubled the kinetic energy gets quadrupled. If two cars, one travelling at 60mph and the other at 30mph the kinetic energy of the former car is four times that of the latter. Thus, the possibility of death increases by about four times too!
  • Kinetic energy cannot be negative; it must either be zero or positive. Velocity can be negative or positive but kinetic energy is at all times positive.
  • K.E. is not a vector unit. The direction of a projectile does not matter. What matters is the velocity it’s thrown with.

Stay tuned with Byju’s to learn more about kinetic energy, energy and much more.


Practise This Question

A 50 g bullet moving with velocity 10 m/s strikes a block of mass 950 g at rest and gets embedded in it. The loss in kinetic energy will be