Question

A ball with a mass of `3 kg` moving at `8 m/s` hits a still ball with a mass of `7 kg`. If the first ball stops moving, how fast is the second ball moving?

Answer 1

`24/7` m/s

Explanation:

Momentum Conservation: `\vec{P_{1i}}+\vec{P_{2i}} = \vec{P_{2i}}+\vec{P_{2f}}`,

Objects at rest have zero momentum,

`m_1.v_{1i}+0=0+m_2.v_{2f}`

`v_{2f}=(m_1/m_2)v_{1i}=(\frac{3kg}{7kg}).(8m/s)=24/7 m/s`