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?

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Answer 1 · 2018-03-17T09:44:17

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

#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#

Answer 2 · 2018-03-17T09:44:44

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#