By what fraction does the mass of a boy increase when he starts running at a speed of `12 km h ^(-1)?

Explanation

Let initial mass be m ` = 1 /2 mv^(2) = E `
`Delta E = 1 / 2 m (12 xx 5 / 18) ^(2) `
` m xx 50 / 9 `
` Delta m = E / c^(2) `
`Delta m = m xx 50 / 9 xx 9 xx 10^(16) `
` Delta m / m = 50 / 81 xx 10^(16) `
` = 50 / 81 xx 10^(16) = 6.17 xx 10^(-16)` .