A ball with a mass of 3 kg3kg moving at 4 m/s4ms hits a still ball with a mass of 8 kg8kg. If the first ball stops moving, how fast is the second ball moving?

2 Answers
Apr 11, 2018

3/2 or 1.5m/s32or1.5ms

Explanation:

P=mv

Momentum stay the same before and after a collision

(3)(4) = (3)(0)+(8)(v)(3)(4)=(3)(0)+(8)(v)

v=12/8=3/2v=128=32

Apr 11, 2018

1.5 \ "m/s"

Explanation:

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

m_1u_1+m_2u_2=m_1v_1+m_2v_2

  • 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 got,

3 \ "kg"*4 \ "m/s"+8 \ "kg"*0 \ "m/s"=3 \ "kg"*0 \ "m/s"+8 \ "kg"*v_2

v_2=(12color(red)cancelcolor(black)"kg""m/s")/(8color(red)cancelcolor(black)"kg")

=1.5 \ "m/s"