A ball with a mass of 5 kg moving at 9 m/s hits a still ball with a mass of 8 kg. If the first ball stops moving, how fast is the second ball moving?

2 Answers
Mar 17, 2018

The velocity of the second ball after the collision is =5.625ms^-1

Explanation:

We have conservation of momentum

m_1u_1+m_2u_2=m_1v_1+m_2v_2

The mass the first ball is m_1=5kg

The velocity of the first ball before the collision is u_1=9ms^-1

The mass of the second ball is m_2=8kg

The velocity of the second ball before the collision is u_2=0ms^-1

The velocity of the first ball after the collision is v_1=0ms^-1

Therefore,

5*9+8*0=5*0+8*v_2

8v_2=45

v_2=45/8=5.625ms^-1

The velocity of the second ball after the collision is v_2=5.625ms^-1

Mar 17, 2018

Initial momentum of the system was 5×9+8×0 Kgms^-2

After the collision momentum was 5×0+8×v Kgms^-2 where,v is the velocity of the 2nd ball after collision.

So,applying law of conservation of momentum we get,

45=8v

Or, v=5.625 ms^-1