Ball $$A$$ of mass 1 kg moving along a straight line with a velocity of $$4 \mathrm{~ms}^{-1}$$ hits another ball $$B$$ of mass 3 kg which is at rest. After collision, they stick together and move with the same velocity along the same straight line. If the time of impact of the collision is 0.1 s then the force exerted on $$B$$ is

Two balls $$A$$ and $$B$$, of masses $$M$$ and $$2 M$$ respectively collide each other. If the ball $$A$$ moves with a speed of $$150 \mathrm{~ms}^{-1}$$ and collides with ball $$B$$, moving with speed $$v$$ in the opposite direction. After collision if ball $$A$$ comes to rest and the coefficient of restitution is 1 (one), then the speed of the ball $$B$$ before it collides with ball $$A$$ is