Question

How much work should be done on a bicycle of mass 20 kg to increase its speed from 2 m s-1 to 5 m s-1 ? (Ignore air resistance and friction).​

Answer 1

Given:-

• Mass,m = 20 kg

• velocity of bicycle,v1 = 2 m/s

• velocity of bicycle,v2 = 5 m/s

To be calculated:-

Calculate the work done.

Solution:-

Case 1 :

We have,

• Mass,m = 20 kg

• velocity of bicycle, v1 = 2 m/s

Kinetic energy = 1/2 × m × (v1)²

★ Putting the values in the above formula,we get:

= 1/2 × 20 × ( 2 )²

= 1/2 × 20 × 4

= 10 × 4

= 40 J

Case 2 :

We have,

• Mass,m = 20 kg

• Velocity of bicycle,v2 = 5 m/s

Kinetic energy = 1/2 × m × ( v2 )²

★ Putting the values in the above formula,we get:

= 1/2 × 20 × ( 5 )²

= 1/2 × 20 × 25

= 10 × 25

= 250 J

Now,

★ Work done = Change in kinetic energy

= 250 J - 40 J

= 210 J

Thus,the work done is 210 joules.