A ball with a mass of #8 kg# moving at #14 m/s# hits a still ball with a mass of #4 kg#. If the first ball stops moving, how fast is the second ball moving?

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Answer 1 · 2018-03-29T07:04:37

See explanation.

The momentum of 2 balls should be the same before and after the collision.

Before the collision we have:

#v_1=14# and #v_2=0#.

Since the masses are:

#m_1=8# and #m_2=4# we can write that:

#m_1v_1+m_2v_2=m_1v_1'+m_2v_2'#

The first ball stops, so the velocity #v_1'=0#.

If we substitute the data we get:

#8*14+4*0=8*0+4*v_2'#

#8*14=4*v_2'#

#v_2'=(8*14)/4=2*14=28#

Answer: The velocity of the second ball is #v_2'=28 m/s#

Answer 2 · 2018-03-29T07:06:30

The velocity of the second ball after the collision is #=28ms^-1#

#m_1u_1+m_2u_2=m_1v_1+m_2v_2#

The mass the first ball is #m_1=8kg#

The velocity of the first ball before the collision is #u_1=14ms^-1#

The mass of the second ball is #m_2=4kg#

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,

#8*14+4*0=8*0+4*v_2#

#4v_2=112#

#v_2=112/4=28ms^-1#

The velocity of the second ball after the collision is #v_2=28ms^-1#