Question

certain force acting on a 20 kg mass changes its velocoty from 5m/to 2m/s calculate the work done

Answer 1

-Mass of an object m= 20 kg,Initial velocity u = 5m/sand final velocity v = 2m/s

.·. Initial kinetic energy of object E1 = ½ mu²= ½ x 20 x (5)² = 250 J

And final kinetic energy of object E2 = ½ mv²= ½ x 20 x (2) ² = 40 J

.·. Loss in kinetic energy = E1 – E2 = 250 – 40 = 210 J

Work done by the force W = Change in kinetic energy = -210 J

The negative sign of work shows that there is decrease in kinetic energy of the mass.

Answer 2

mass= 20kg
u=5m/s
v=2m/s

k.e= m×(v-u)
= 1/2×20×(2-5)2
=1/2×20×(4-25)
=1/2×20×-21
=1/2×-420
=-210