Answer to Question #252820 in Mechanics | Relativity for yago

Question

A bodyvof mass 12kg travelling at 4.2m/s collide with a sound body of mass 18kg at rest. Calculate their common velocity

Answer 1

Their common velocity can be found from momentum conservation:

$$mv+M*0=(m+M)u,\\\space\\ u=mv/(m+M)=1.68\text{ kg m/s}.$$