# Dynamics and Equilibrium - Physics Learning 4

Practice Dynamics and Equilibrium questions with answers. This prep guide includes questions like, what is momentum of an isolated system?, why recoil of gun is much smaller than velocity?, on what factors force of friction depends?, why does force of friction oppose motion?, what is force of limiting friction? and others below.

## Dynamics and Equilibrium Learning 4

Question: What is momentum of an isolated system?

Answer: A system is said to be isolated if net force acting on it is zero. If there is no external and unbalanced force then momentum of the system is constant. Hence, the momentum of an isolated system is always conserved.

Question: Why recoil of gun is much smaller than velocity?

Answer: It is due to the law of conservation of momentum. The total momentum of the gun and bullet after firing is equal to the total momentum of the gun and bullet before firing. Mathematically MV = -mv. The negative sign indicates that the direction of recoil is opposite to the velocity of bullet. Since, the mass of gun is much larger so the velocity of recoil is much smaller as compare to the velocity of bullet.

Question: On what factors force of friction depends?

Answer: Friction is a force which opposes the motion of any object. This force depends upon many factors including nature of surfaces in contact and the pressing force between the surfaces in contact.

Question: Why does force of friction oppose motion?

Answer: Friction exists between the surfaces in contact. No real surface is perfectly smooth. Every surface has small pits and bumps. When two rough surfaces come in contact with each other they forms sort of cold welds. These cold welds resist the surfaces to slide over each other. Hence, generating force of friction.

Question: What is force of limiting friction?

Answer: The frictional force cannot increase to a certain maximum value. It can't be increased beyond this level. This maximum value of friction is known as the force of limiting friction.