Spark image

Kinetic energy formula

Question: Why is the mass halved in the formula for Kinetic Energy (KE = mv2)?

Answer:

Lets imagine an object (mass m) moving with velocity u and being brought to rest by a steady retarding force F in a distance s.

Work done by the retarding force = Fs = kinetic energy lost (converted to heat)

But using v2 = u2 + 2as with v = 0 and a = -F/m (- sign denotes deceleration) we have:

u2 = 2as = 2F/m so F = [mu2]/2s

Therefore: Kinetic energy = Fs = [mu2]/2s = [mu2]/2

So that is why the half appears in the formula.
 

A VERSION IN WORD IS AVAILABLE ON THE SCHOOLPHYSICS USB
 
 
 
 
© Keith Gibbs 2020