Question

certain force acting on a 20kg mass change its velocity from 5m/s to 2m/s calculate the work done by the force.

Answer 1

I think the work done by the forces 120

Answer 2

Solutions:

We know that whenever work is done, an equal amount of energy is used up. So, the work done in this case will be equal to the change in kinetic energy of bicycle when its speed changes from 2 m/s to 5 m/s.

(a) In the first case;

Mass of bicycle, m = 20 kg

And, speed of bicycle, v = 2 m/s

So, kinetic energy, Ek = 1/2mv^2

=> 1/2 × 20 × (2)^2

=> 10 × 4

=> 40 J

(b) In the second case;

Mass of bicycle, m = 20 kg

And, speed of bicycle, v = 5 m/s

So, kinetic energy, Ek = 1/2mv^2

=> 1/2 × 20 × (5)^2

=> 10 × 25

=> 250 J

Now, Work done = Change in kinetic energy.

=> 250 - 40

=> 210 J

Thus, the work done is 210 J.