Question

A ball of mass 0.5 kg slows down from a speed of 5 m/s so that of 3 m/s. Calculate the change in kinetic energy of the ball. State your answer giving proper units.

Answer 1

Mass of the ball, (m) = 0.5 kg
Initial velocity, (v₁) = 5 m/s
Final velocity, (v₂) = 3 m/s
So, initial kinetic energy can be calculated as,
`K.E = 1/2 mv^2`
Therefore, initial kinetic energy,
`(K.E)_1 = 1/2 xx 0.5 xx 5^2` J
= 6.25 J
Similarly, final kinetic energy,
`(K.E)_2 = 1/2 xx 0.5 xx 3^2` J
= 2.25 J
So, Work done = Change in kinetic energy
Therefore work done,
Work done = (KE)₂ – (KE)₁
                  = (2.25 – 6.25) J
                   = – 4 J
A negative sign shows that the force applied is opposite to the direction of motion of the body.