English Medium कक्षा ९ - CBSE Question Bank Solutions

Which physical principle is involved in the working of a jet aeroplane ?

Name the principle on which a rocket works.

Fill in the following blanks with suitable words :

 Momentum is a _____________ quantity. Its unit is _____________.

Fill in the following blanks with suitable words :
In collisions and explosions, the total _____________ remains constant, provided that no external _____________ acts.

A 10 g bullet travelling at 200 m/s strikes and remains embedded in a 2 kg target which is originally at rest but free to move. At what speed does the target move off ?

A body of mass 2 kg is at rest. What should be the magnitude of force which will make the body move with a speed of 30 m/s at the end of 1 s ?

The velocity of a body of mass 10 kg increases from 4 m/s to 8 m/s when a force acts on it for 2 s.
(a) What is the momentum before the force acts ?
(b) What is the momentum after the force acts ?
(c) What is the gain in momentum per second ?
(d) What is the value of the force ?

A gun of mass 3 kg fires a bullet of mass 30 g. The bullet takes 0.003 s to move through the barrel of the gun and acquires a velocity of 100 m/s. Calculate:

1. the velocity with which the gin recoils.
2. the force exerted on gunman due to recoil of the gun

Name the law involved in the following situation :

the sum of products of masses and velocities of two moving bodies before and after their collision remains the same.

Explain why, a cricket player moves his hands backwards while catching a fast cricket ball.

A 150 g ball, travelling at 30 m/s, strikes the palm of a player’s hand and is stopped in 0.05 second. Find the force exerted by the ball on the hand.

State the law of conservation of momentum.

Discuss the conservation of momentum in each of the following cases :
(i) a rocket taking off from ground.
(ii) flying of a jet aeroplane.

An unloaded truck weighing 2000 kg has a maximum acceleration of 0.5 m/s². What is the maximum acceleration when it is carrying a load of 2000 kg ?

Why are car seat-belts designed to stretch some what in a collision ?

The troops (soldiers) equipped to be dropped by parachutes from an aircraft are called paratroopers. Why do paratroopers roll on landing ?

Why would an aircraft be unable to fly on the moon ?

Explain why it is possible for a small animal to fall from a considerable height without any injury being caused when it reaches the ground.

A boy of mass 50 kg running at 5 m/s jumps on to a 20 kg trolley travelling in the same direction at 1.5 m/s. What is their common velocity ?

A girl of mass 50 kg jumps out of a rowing boat of mass 300 kg on to the bank, with a horizontal velocity of 3 m/s. With what velocity does the boat begin to move backwards ?