The kinetic energy of an object is its energy of motion. Kinetic energy depends on the mass and speed. A car will have more kinetic energy when it has a higher speed, while a massive lorry will have more kinetic energy than a car of the same speed.

To derive an expression for the kinetic energy, consider the work done by a force on an object of mass initially at rest. According to Newton's Second Law, the force is equal to mass times acceleration ( ). If the object moves by a distance , the work done will be

Using the equation with the initial velocity , we have

Since the work done is equal to the energy transferred, we can identify as the kinetic energy of an object:

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 Example

Calculate the kinetic energy for the following objects:

1. A 747 aeroplane of mass flying at a speed of 1000 .

2. A car of 1000 kg travelling at 100 .

3. A man of 50 kg walking at 2 .

4. An arrow of mass 0.03 kg shot at a speed of 60

5. A bowling of 6 kg moving at 2

Solution