Question

A ball with a mass of `6 kg` moving at `4 m/s` hits a still ball with a mass of `3 kg`. If the first ball stops moving, how fast is the second ball moving?

Answer 1

`8` meters per second

Explanation:

We use the law of conservation of momentum, which states that,

`m_1u_1+m_2u_2=m_1v_1+m_2v_2`

where:

• `m_1,m_2` are the masses of the two objects

• `u_1,u_2` are the initial velocities of the two objects

• `v_1,v_2` are the final velocities of the two objects

So, here we get:

`6 \ "kg"*4 \ "m/s"+3 \ "kg"*0 \ "m/s"=6 \ "kg"*0 \ "m/s"+3 \ "kg"*v_2`

`24 \ "kg m/s"=3 \ "kg"*v_2`

`v_2=(24color(red)cancelcolor(black)"kg""m/s")/(3color(red)cancelcolor(black)"kg")`

`=8 \ "m/s"`