Given
m1 = 15kg
vi1 = +20 m/s
vf1 = +5 m/s
m2 = 10 kg
vi2= -15 m/s
vf2 = ?
Procedure
Conservation of momentum, general law of physics according to which the quantity called momentum that characterizes motion never changes in an isolated collection of objects; that is, the total momentum of a system remains constant.
[tex]\begin{gathered} m_1v_{i1}+m_2v_{i2}=m_1v_{f2}+m_2v_{f2} \\ 15kg\cdot20m/s+10\operatorname{kg}\cdot-15m/s=15\operatorname{kg}\cdot5m/s+10\operatorname{kg}\cdot v_{f2} \\ 150-75=10v_{f2} \\ v_{f2}=75/10 \\ v_{f2}=7.5\text{ m/s} \end{gathered}[/tex]The speed of the 10kg Ball is 7.5m/s
