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A body of mass 10 kg is moving with a velocity 20m s-1. If the mass of the body is doubled and its velocity is halved, find: (i) the initial kinetic energy, and (ii) the final kinetic energy.
A body of mass 10 kg is moving with a velocity 20m s-1. If the mass of the body is doubled and its velocity is halved, find: (i) the initial kinetic energy, and (ii) the final kinetic energy.
Class 10 | ICSE | Physics | Selina | Work Energy
A body of mass 10 kg is moving with a velocity 20m s-1. If the mass of the body is doubled and its velocity is halved, find: (i) the initial kinetic energy, and (ii) the final kinetic energy.

Solutions:

According to the question –

Let initial Mass be denoted by m1 = 10 kg and

Velocity, v1 is 20 m / s

Then, final mass is m2 = 2 × 10 kg and

Velocity, v2 is  20 / 2 = 10 m / s

By using the expression of the kinetic energy, we get –

For initial kinetic energy,

K1 = 1 / 2 × mass × (velocity)2

= 1 / 2 × 10 × (20)2 = 1 / 2 × 10 × 20 × 20

= 2000J

For, final kinetic energy,

K2 = 1 / 2 × mass × (velocity)2

= 1 / 2 × 20 × (10)2 = 1 / 2 × 20 × 10 × 10

= 1000J

Therefore, the ratio of initial to final kinetic energy is

 K1 / K2 = 2000 / 1000 = 2 / 1

 K1 / K2  = 2: 1

i

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