When a missile is fired from a tank,it gets a momentum of $2000 \ kg \ m \ s^{-1}$. If the velocity of the missile is $50 \ m \ s^{-1}$,what will be its mass (in $kg$)?

$(a)$ State Newton's second law of motion. Use this law to find a method to measure force acting on an object.
$(b)$ From a rifle of mass $4 \ kg$,a bullet of mass $50 \ g$ is fired horizontally with an initial velocity of $40 \ m \ s^{-1}$. Calculate the initial recoil velocity of the rifle.

Newton's first law of motion is also called the law of inertia. Why?

$A$ man is at rest in the middle of a pond on perfectly smooth ice. He can get himself to the shore by making use of Newton's:

Name and state the action and reaction in the following cases:
$(i)$ Firing of a bullet from a gun.
$(ii)$ Hammering a nail.
$(iii)$ $A$ book lying on a table.
$(iv)$ Moving rocket.
$(v)$ $A$ person moving on the floor.
$(vi)$ $A$ moving train colliding with a stationary train.

According to Newton's third law,every force is accompanied by an equal and opposite force. How then can anything move?