Science (English Medium) कक्षा ११ - CBSE Question Bank Solutions

What is the average friction force when a person has a usual 1 km walk?

Why is it difficult to walk on solid ice?

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 half 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 sandwitch a 20 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 the 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? (c) Why does the experiment fail if the card is gently pushed?

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

You are standing with your bag in your hands, on the 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 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.

While walking on ice, one should take small steps to avoid slipping. This is because smaller steps ensure

Consider the situation shown in figure. The wall smooth but the surface of A and B in contact are rough. The friction on B due to A in equilibrium

Suppose all the surface in the previous problem are rough. The direction of friction of B due to A

A spring-mass system oscillates with a frequency v. If it is taken in an elevator slowly accelerating upward, the frequency will

A spring-mass system oscillates with a car. If the car accelerates on a horizontal road, the frequency of oscillation will

A piece of wood is taken deep inside a long column of water and released. It will move up

A solid sphere falls with a terminal velocity of 20 m s⁻¹ in air. If it is allowed to fall in vacuum, 

A solid sphere moves at a terminal velocity of 20 m s⁻¹ in air at a place where g = 9.8 m s⁻². The sphere is taken in a gravity-free hall having air at the same pressure and  pushed down at a speed of 20 m s⁻¹.

(a) Its initial acceleration will be 9.8 m s⁻² downward.
(b) It initial acceleration will be 9.8 m s⁻² upward.
(c) The magnitude of acceleration will decrease as the time passes.
(d) It will eventually stop

Which of the following gases has maximum rms speed at a given temperature?

Suppose a container is evacuated to leave just one molecule of a gas in it. Let v_a and v_rms represent the average speed and the rms speed of the gas.

The rms speed of oxygen at room temperature is about 500 m/s. The rms speed of hydrogen at the same temperature is about