A ball with a mass of 8 kg moving at 14 m/s hits a still ball with a mass of 2 kg. If the first ball stops moving, how fast is the second ball moving?

1 Answer
Gagandeep Singh
Dec 26, 2015

56m/s.

Explanation:

We need to consider here the conservation of linear momentum. The law of conservation of linear momentum states that the total momentum of an isolated system is conserved, i.e.,
m_1v_1 + m_2v_2 = m_1v_1^' + m_2v_2^'
where m's are the masses of the two objects, v's are the magnitudes of velocities before collision and v^''s are the velocities of the objects after collision. We assume that the velocities are non-relativistic so that the masses remain constant.

For a perfectly inelastic collision, as is in the current problem,
v_2 = 0 & v_1^' = 0
Therefore, we have, m_1v_1 = m_2v_2^'.

Thus, given that m_1 = 8kg, m_2 = 2kg and v_1 = 14m/s,
v_2^' = m_1v_1/m_2 = 8**14/2 = 56m/s.

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