Learn about kinetic and gravitational potential energy.

Part of

All moving objects have kinetic energy, .

The KE of an object depends on its:

- mass
- speed

**Calculating kinetic energy**

The kinetic energy of a moving object can be calculated using the equation:

Kinetic energy = x mass x (speed)^{2}

Kinetic energy = mv^{2}

or

= mv^{2}

where:

= kinetic energy in joules, J

m = mass in kg

v = speed in m/s

- Question
What is the kinetic energy of a 1000 kg car travelling at 5 m/s?

= mv

^{2}m = 1000 kg

v = 5 m/s

= 1000 kg x (5 m/s)

^{2}= 12,500 J

The car has 12,500 J of kinetic energy

- Question
A car of mass 1200 kg, travelling at a steady speed, has a kinetic energy of 175 kJ. What is the speed of the car?

= mv

^{2}The car has 175 kJ of kinetic energy. This must be converted into J to use in the equation for kinetic energy.

175 kJ = 175,000 J

= 175,000 J

m = 1200 kg

175,000 = x 1200 kg x v

^{2}175,000 = 600 kg x v

^{2}v

^{2}=v

^{2}= 291.67v = \sqrt{291.67}

v = 17.1 m/s

The car has a speed of 17.1 m/s.