   Kinetic energy is energy of motion. The kinetic energy of an object is the energy it possesses because of its motion.

Kinetic energy is an expression of the fact that a moving object can do work on anything it hits; it quantifies the amount of work the object could do as a result of its motion. The total mechanical energy of an object is the sum of its kinetic energy and potential energy.

Example

A rocket of mass 1.5x10^4 kg accelerates at 220m/s/s for 29s from an initial speed of 5200m/s.

(a) How fast will be rocket be travelling after the 29s?

Solution:

Use v =v ' + at

v = Final Velocity

v ' = Initial Velocity

a = Acceleration

t = Time

v = v ' + at

v = (5200 m/s) + (220 m/s/s)(29 s)

v = 11580 m/s

Part 2 of the Example

(b) How much Kinetic Energy has the rocket gained?

Solution:

Calculate the kinetic energy of the rocket both before and after the acceleration and work out the difference.

Solution:

Use KE = 1/2 mv^2

KE = Kinetic Energy

m = Mass

v = Velocity

KE = 1/2 mv^2

Initial Kinetic Energy:

KE = 1/2 (1.5x10^4 kg)(5200m/s)^2

KE = 2.028 x 10^11 J

Final Kinetic Energy:

KE = 1/2 (1.5x10^4 kg)(11580 m/s)^2

KE = 1.006 x 10^12 J

Change in Kinetic Energy

Final Kinetic Energy - Initial Kinetic Energy = Change in Kinetic Energy

1.006 x 10^12 J - 2.028 x 10^11 J = 8.032 x 10^11 J

Example problem provided by Mr Mackenzie