Energy is something that gives the body the capacity to do the work. Energy has many forms like kinetic energy, potential energy, mechanical energy, nuclear energy, solar energy. It has many formulas, some of the popular ones are:

1. Potential energy is given by,
P.E = mgh.

Where, m is the mass, g is the gravitational force, h is the height.

2. Kinetic energy is given by,
K.E = $\frac{1}{2}$ mv2

Where, m is the mass, v is the velocity.

3. The mechanical energy formula is given by,
M.E = F $\times$ D.
Where F is the force, D is the displacement.

4. Einstein's mass energy formula is given by,
E = mc2
Where m is the mass, c is the velocity of light.

5. The energy of a photon is given by,
E = $\frac{hc}{\lambda}$.
Where,
h = Planck's constant, 
c = the speed of light, 
$\lambda$ = the wavelength of light.

Below are given some problems on energy:

Question 1: John is of mass 22 kg and runs with velocity of 2m/s. Calculate the kinetic energy he has in motion.
Solution:
Given: Mass m = 22 kg, velocity v = 2m/s

The kinetic energy is given by,
K.E = $\frac{1}{2}$ mv2

K.E = $\frac{1}{2}$ $\times$ 22 kg $\times$ (2 m/s)2

K.E = 44 J.

Therefore, john runs with 44 J of kinetic energy.

Question 2: A force of 200 N is applied on a body and it get displaced by 2m. Calculate the energy it has.
Solution:
Given : Force F = 200 N, displacement D = 2m

The energy is given by,
E = F.D
E = 200 N $\times$ 2 m
E = 400 J.

Therefore, the given body has 400 J of energy.