Question

Two billiard balls of equal mass move at right angles and meet at the origin of an xy coordinate system. Ball A is moving upward along the y axis at vA = 1.9m/s , and ball B is moving to the right along the x axis with speed vB = 5.4m/s . After the collision, assumed elastic, ball B is moving along the positive y axis(Figure 1) . What is the final direction of ball A? What are their two speeds?

Answer 1

conservation of momentum along x axis direction

m*5.4=m*va

va=5.4m/s

conservation of momentum along y axis direction

m*1.9=m*vb

vb=1.9m/s

So, we can get Vbar1y= 5.4ibar kg m/s, Vbar2y= 1.9jbar m/s.