Question

A 47.4 kg student runs down the sidewalk and jumps with a horizontal speed of 4.20 m/s onto a stationary skateboard. The student and skateboard move down the sidewalk with a speed of 3.95 m/s. What is the mass of the skateboard?

Answer 1

The mass of the skateboard is `=3kg`

Explanation:

There is conservation of momentum

`m_1u_1+m_2u_2=(m_1+m_2)v`

The mass of the student is `m_1=47.4kg`

The mass of the skateboard is `=m_2 kg`

The initial speed of the student is `u_1=4.2ms^-1`

The speed of the student and skateboard is `v=3.95ms^-1`

`47.4xx4.2+m_2xx0=(47.4+m_2)xx3.95`

`47.4+m_2=47.4*4.2/3.95=50.4`

`m_2=50.4-47.2=3kg`