Question

A 66.0-kg boy and his 45.0-kg sister, both wearing roller blades, face each other at rest. The girl pushes the boy hard, sending him backward with a velocity 2.80 m/s toward the west. Ignore friction. (a) Describe the subsequent motion of the girl.

Answer 1

Answer:

the girl moves towards right with a velocity of 4.1m/s

Explanation:

Since the system is isolated the momentum of the system is conserved

Initial momentum = Final Momentum

Since initially the system is at rest thus $\overrightarrow{p_{i}}=0$

Now the final momentum of boy = $m_{boy}×velocity$

$\overrightarrow{p_{boy}}=66.0\times -2.80m/s\\\\\overrightarrow{p_{boy}}=-184.8kgm/s$

Now for girl let the velocity = u hence her moumentum is 45$\times u$

Thus equating final momentum to zero we have

$-184.8kgm/s$+$45\times u = 0$

$u=\frac{184.8}{45}m/s$

hence $u=4.1m/s$

Thus the girl moves towards right with a velocity of 4.1m/s