A racing dog is initially running at 20.0 m/s, but is slowing down.

Question

Question: How fast is the dog moving when its kinetic energy has been reduced by half?
Question: By what fraction has its kinetic energy been reduced when its speed has been reduced by half?

Answer 1

Use the fact that
kinetic energy = (1/2)MV^2.

For half the kinetic energy, the V^2 term must be reduced from 400 to 200, in this case.

That means V = 14.14 m/s

If you reduce speed by half, you have 1/4 the kinetic energy