Lesson 5, Topic 3
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# Meaning of Potential and Kinetic Energy

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Mechanical Energy can be divided into two, Potential and Kinetic Energy;

### Potential Energy:

Potential energy may be defined as stored energy. It is the energy of a stationary object due to its position. It is the energy one possesses when one is not moving. It can also be said to be the energy an object or body possesses by virtue of its position, that is when the body is at rest.

Potential energy = mgh

Where m = mass of the object  g = gravity, h = meter (distance).

A ball resting on a stool has potential energy.

What happens to the potential energy if the ball is placed on a higher stool?

Answer: The potential energy is greater if the position of the ball is higher. We can say that the ball has the potential to cause more damage. In other words, the greater the distance the higher the potential energy.

### Example 1:

i. Find the potential energy of an object of mass 20 kg placed on a table of 8 m height (g = 10m/s2)

Solution:

Potential energy = mgh

= 20 x 10 x 8

= 1600 Joules.

ii. Find the potential energy, if the same object of mass 20kg is placed higher, on a table of 15 m height (g = 10m/s2)

Solution:

Potential energy = mgh

= 20 x 10 x 15

= 3000 Joules.

### Kinetic Energy:

Kinetic energy is the energy a body possessed by virtue of its motion. Moving objects possess kinetic energy. Kinetic energy is therefore the energy possessed by a body in motion i.e energy of motion.

The amount of kinetic energy possessed by a body is dependent on the mass and velocity with which it is moving.

Examples of kinetic energy include riding a bike, dancing, a stone falling, car driving, etc.

Kinetic energy (K.E) = $$\frac{1}{2} \scriptsize mv^2$$

where;

M = mass of the object

V = velocity of the object.

As an object moves faster its kinetic energy increases.

### Example 2:

An arrow of mass 10 kg is moving at a constant velocity of 15 m/s. Calculate its kinetic energy.

Solution:

Kinetic Energy = $$\frac{1}{2} \scriptsize mv^2$$

= $$\frac{1 \: \times \: 10 \: \times \: 15^2}{2} \scriptsize$$

= $$\frac{1 \: \times \: 10 \: \times \: 225}{2} \scriptsize$$

= 5 x 225

= 1125 Joules.

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