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.


 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?


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?


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


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