Correct Answer: Option C

Explanation

Given: mass of boy = 40 kg = m\(_b\), mass of skateboard = ? = m\(_k\), speed of skateboard v\(_x\) = - 20 m/s, speed of boy v\(_y\) = 1.5 m/s

Both the skateboard and the boy were initially at rest.

The total momentum before and after the jump must be equal.

0 = m\(_b\) x v\(_y\) + m\(_k\) x  v\(_x\)

0 = 40 x 1.5  +  m\(_k\) x (-20)

0 = 60 - 20m\(_k\)

20m\(_k\) = 60

m\(_k\) = \(\frac{60}{20}\) = 3 kg.

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