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.
![\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}]()
The speed of the 10kg Ball is 7.5m/s