Find work done by friction if block reaches to the end with constant velocity

A ball of mass $m$ strikes the inclined face of the wedge normally with speed $v_0$. The wedge is at rest on a rough horizontal surface before collision. The conservation of momentum is applicable for the event of collision for

$(i)$ $m$ as system, along $Y'$
$(ii) $ $M$ as system, along $Y'$
$(iii)$ $(M + m)$ as system, along $X$
$(iv)$  $(M + m)$ as system, along $Y$
Which of the following is correct?

Six identical balls are lined in a straight groove made on a horizontal frictionless surface.  Two similar balls each moving with a velocity $v$ collide elastically with the row of $6\, balls$ from left. What will happen ?

A particle $P$ moving with speed $v$  undergoes a head -on elastic collision with another particle $Q$ of identical mass but at rest. After the collision

A body $x$ with a momentum $p$ collides with another identical stationary body $y$ one dimensionally. During the collision $y$ gives an impulse $J$ to body $x$. Then coefficient of restitution is

A light particle moving horizontally with a speed $v_1$ strikes a very heavy block moving in the same direction with a speed $v_2$. The collision is elastic. After the collision, the velocity of particle is :-