Two boys on skateboards are facing each other. They push off, the first boy (mass: 43.8 kg) traveling backward at 2.1 m/s. If the second boy is now traveling at 3.09 m/s, what is his mass?

The mass of the second boy is, m = 29.77 kg

Explanation:

Given data,

The mass of first boy, M = 43.8 kg

The velocity of first boy, V = - 2.1 m/s

The velocity of second boy, v = 3.09 m/s

Then mass of second boy, m = ?

According to the law of conservation of momentum,

mv + MV = 0

m = - MV / v

Substituting the values,

m = 43.8 x 2.1 / 3.09

m = 29.77 kg

Hence, the mass of the second boy is, m = 29.77 kg