Question

a ball of mass 15 kg moving at +20 m/s collides head-on with another ball of mass 10 kg moving at -15 Ms. if after collision the speed of the 15 kg ball is +5 m/s determine the speed of the 10 kg ball

Answer 1

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