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## Chapter: 11th Physics : UNIT 3 : Laws of Motion

Physics : Laws of Motion : Book Back Exercise, Example Numerical Question with Answers, Solution : Conceptual Questions Answers

Laws of Motion | Physics

Conceptual Questions

1. Why it is not possible to push a car from inside?

(i) When you push a car from inside, the reaction force of your pushing is balanced out by your body moving backward.

(ii) The seat behind you pushes against to bring things to static equilibrium.

2. There is a limit beyond which the polishing of a surface increases frictional resistance rather than decreasing it why?

(i) Due to excessive polishing, more molecules of the two surfaces come closer. Thus they form more bonds and offer great resistances.

(ii) Because friction arises due to molecular adhesion i.e. due to electrostatic forces.

3. Can a single isolated force exist in nature? Explain your answer.

No, a single isolated force cannot exist in nature because it violates the Newton's third law.

4. Why does a parachute descend slowly?

A parachute is a device used to slow down on object that is falling towards the ground. When the parachute opens, the air resistance increases. So the person can land safely.

5. When walking on ice one should take short steps. Why?

It is to avoid slipping. Smaller step causes more normal force and thereby more friction.

6. When a person walks on a surface, the frictional force exerted by the surface on the person is opposite to the direction of motion. True or false?

False. The frictional force exerted by the surface is not opposite to the direction of motion.

7. Can the coefficient of friction be more than one?

Yes, Î¼ > 1, friction is stronger than normal force.

8. Can we predict the direction of motion of a body from the direction of force on it?

In free body diagrams, the force of friction is always parallel to the surface of contact. The force of kinetic friction is always opposite the direction of motion.

9. The momentum of a system of particles is always conserved. True or false?