A body of mass $M$ moving with a velocity $u$ collides with another of mass $m$ which rests on a table. Both the balls are perfectly elastic and smooth and the the body of $m$ is driven in a direction making an angle $\theta$ with the previous line of motion of $M$. Show that its velocity is $$\frac{2M}{M+m}u\cos{\theta}.$$
I have some doubt to understand the problem. It seams to me that the collision is direct (not oblique). Let after impact, $v_1$, $v_2$ are the velocities of bodies of masses $M$ and $m$ respectively.
I am unable to understand the line "the the body of $m$ is driven in a direction making an angle $\theta$ with the previous line of motion of $M$"
What will be the angles after the impact with the line of centers. Please help me.
It seems to me that, I have to find $v_2$.
I want to apply then the Newton's experimental law and conservation of linear momentum.
The collision is oblique.$M$ comes in from point $A$, the impact is at $B$ and leaves on the way to $C$. $m$ starts at $B$ and leaves on the way to $D$. The vector to $E$ is the continuation of $M$'s initial motion. $\theta$ is shown. You need to apply momentum conservation in each axis as well as energy conservation.