Work and Energy — Question 4

Given,

Initial velocity u = 5 ms^-1

Mass of the body = 20 kg

Final velocity v = 2 ms^-1

Initial kinetic energy

E_i = $\dfrac{1}{2}$mu²

Substituting we get,

E_i = $\dfrac{1}{2}$ x 20 x 5²
= 10 × 25
= 250 J

Final kinetic energy

E_f = $\dfrac{1}{2}$mv²
= $\dfrac{1}{2}$ x 20 x 2²
= 10 × 4
= 40 J

As, Work done = Change in kinetic energy = E_f – E_i

Work done = 40 J - 250 J

Work done = -210 J

Hence, work done by the force = -210 J.