WAEC Physics 2024 Paper

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.