$(a)$ Name the force that keeps the object moving in a circular path with constant acceleration.
$(b)$ What would happen if this force is absent?

$(a)$ Define momentum of a body.
$(b)$ $A$ ball is thrown vertically upward. What is its momentum at the highest point?
$(c)$ State the law of conservation of momentum.

$A$ force can be completely described by

$A$ bullet of mass $m$ is fired from a gun of mass $M$. If the velocity of the bullet is $v$,derive an expression for the recoil velocity of the gun. On which principle is this based?

Name the unbalanced force which slows down a moving bicycle when we stop pedalling it.

Suppose a ball of mass $m$ is thrown vertically upward with an initial speed $v$. Its speed decreases continuously until it becomes zero. Thereafter,the ball begins to fall downward and attains the speed $v$ again before striking the ground. It implies that the magnitude of the initial and final momentum of the ball are the same. Yet,it is not an example of the conservation of momentum. Explain why?