A ball of mass 1kg strikes a wedge of mass 4kg horizontally with a velocity of 10ms^-1 . Just after collision, the velocity of wedge becomes 4 ms^-1 . Friction is absent everywhere and collision is elastic. Then

Collision is elastic so KE is conserved. Let V be the speed of the ball after collision then

$\frac{1}{2}1(10{)}^2=\frac{1}{2}4\left(4^2\right)+\frac{1}{2}1{\mathrm{V}}^2\Rightarrow \mathrm{V}=6\mathrm{m}/\mathrm{s}$
Let J be the impulse between the two during collision.

Apply impulse = change in momentum 

For wedge, we can write

$$\begin{gathered} \Rightarrow \mathrm{Jsin} {30}^0 = \left(4\right)\left(4\right) \\ \Rightarrow \mathrm{J} = 32 \mathrm{N}-\mathrm{s} \end{gathered}$$