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## Saturday, September 5, 2009

### Kinetic energy

Kinetic energy is one if the eight forms of energy. It is simply the energy that a body possesses due to its motion.

The kinetic energy of a body is simply calculated using the equation

Kinetic energy Ek = ½ mv2

Where m is the mass of the mass of the object in kg
v is the velocity of the object in ms-1

As you can see the kinetic energy of the object depends on both the velocity and the mass of the object. So it is possible for an elephant with a large mass to have the same kinetic energy as a small object moving at a high velocity.

Now let us see an example where the kinetic energy of an object is calculated.

Example 1

An elephant of mass 3.00 x 103 kg is moving at a velocity of 3.00 ms-1. What is the kinetic energy of the elephant?

So let us recall that the kinetic energy of the elephant is calculated using the equation

Ek = ½ mv2

Hence the kinetic energy Ek = ½ mv2
= ½(3.00* 103)*(3.00)2
= 13500 J
= 1.35 *104 J

Now you can be given the kinetic energy and be asked to calculate the mass or the velocity. Let us look at a second example.

Example 2

An object has a mass of 4.0 kg and a kinetic energy of 16 J. Determine the velocity of the object.

Ek = ½ mv2
16 = ½ (4.0)*v2

Making v the subject of formula

v2 = (16 *2)/4.0
v = (16*2/4.0)½
v = 2.8 ms-1

Now to test your newly acquired you can do the following questions

1. Calculate the kinetic energy possessed by an aeroplane of mass 3.4 * 105 kg flying at 110 ms.
2. If a body has 3.4 x 105 J of kinetic energy and mass 3.2* 102 kg, what is its velocity?