Question

calculate the kinetic energy of a body of mass 5kg moving with velocity of 10m/s. Also find the ratio of initial kinetic energy and final kinetic energy if I) its mass is double and ii) its velocity is made 3 times
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Answer 1

Given :

Mass of body = 5 kg

Velocity of body = 10 m/s

To Find :

Kinetic energy of the body and ratio of initial kinetic energy and final kinetic energy if

• mass is doubled
• velocity is made 3 times

Solution :

❒ Kinetic energy of an object is the energy that it possesses due to its motion$.$

Formula : k = 1/2 mv²

• k denotes kinetic energy
• m denotes mass
• v denotes velocity

By substituting the given values;

➙ k = 1/2 mv²

➙ k = 1/2 × 5 × 10²

➙ k = 500/2

➙ k = 250 J

A] Mass is doubled :

In this case velocity of body remains constant, so we can say that, k ∝ m

➙ k/k' = m/m'

➙ k/k' = m/2m

➙ k/k' = 1/2

➙ k : k' = 1 : 2

B] Velocity is made three times :

In this case mass of body remains constant, so we cam say that, k ∝ v²

➙ k/k' = v²/v'²

➙ k/k' = v²/(3v)²

➙ k/k' = 1/9

➙ k : k' = 1 : 9