H C Verma Solutions for Chapter: Friction, Exercise 1: QUESTIONS FOR SHORT ANSWER

Why is it difficult to walk on a solid ice?

Can you accelerate a car on a frictionless horizontal road by putting more petrol in the engine? Can you stop a car going on a frictionless horizontal road by applying brakes?

The spring fitted doors close by themselves when released. You want to keep the door open for a long time, say for an hour. If you put a $\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.$ $\mathrm{kg}$ stone in front of the open door, it does not help. The stone slides with the door and the door gets closed. However, if you sandwich a $20 \mathrm{g}$ piece of wood in the small gap between the door and the floor, the door stays open. Explain why, a much lighter piece of wood is able to keep the door open, while a heavy stone fails.

A classroom demonstration of Newton's first law is as follows: A glass is covered with a plastic card and a coin is placed on the card. The card is given a quick strike and the coin falls in the glass. 

(a) Should the friction coefficient between the card and the coin be small or large?

(b) Should the coin be light or heavy? 

Can a tug of war be ever won on a frictionless surface?

Why do tyres have a better grip of the road while going on a level road than going on an incline?

You are standing with your bag in your hands on an ice in the middle of a pond. The ice is so slippery that it can offer no friction. How can you come out of the ice?

When the two surfaces are polished, the friction coefficient between them decreases. But the friction coefficient increases and becomes very large if the surfaces are made highly smooth. Explain.