**Notes**
**Assignments**
**NCERT Solutions**

## VeryShort Questions Type

**1**.During the game of table tennis, if the ball hits a player it does not hurt him. On the other hand when a fast moving cricket ball hits a spectator it may hurt him. State reason.

**2**.Define the first law of motion.

**3**.Why do a backseater moves forward when a fast moving bike is stopped suddenly?

**4**.When a carpet is beaten with a stick it releases dust. Explain why.

**5**.Name the physical quantity that measures inertia. State its SI unit.

**6**.Name the property of bodies by virtue of which they resist a change in their state of rest or of uniform motion.

**7**.What is the momentum of a body of mass 5 kg moving with a velocity of 0.20 m/s.

**8**.Write the net force acting on a bus, of mass 2000 kg, moving with a uniform velocity of 60 km/h.

**9**.State the relation between the momentum of a body and the force acting on it.

**10.**A body of mass 25 kg has a momentum of 125 kg m/s. calculate the velocity of the body.

**11**.Name the physical quantity which is measured/ determined by the rate of change of momentum. Linear momentum.

**12**.What is the mathematical formula and SI unit of momentum?

**13**.What force would be needed to produce an acceleration of 4 m/s2 on a ball of mass 6 kg?

**14**.State Newton’s third law of motion.

**15**.In the collision between a heavier body and a lighter body, if the force experienced by the heavier body is F1 and that by the lighter body is F2, write the relation between F1 and F2.

**16**.Explain why same of the leaves may get detached from a tree if we vigorously shake its branch?

**17**.An object of mass 100 kg is accelerated uniformly from a velocity of 5 ms-1 to 8 ms-1 in 6 s. Calculates the initial and final momentum of the object. Also find the magnitude of force exerted on the object.

**18**.Out of the four physical quantities associated with the motion of an object viz force, velocity, acceleration and momentum which one remains constant for all bodies large or small, undergoing a free fall?

**19**.A runner passes the ground with his fect before he starts his run. Identify action and reaction in this situation.

**20**.An athlete always runs some distance before taking a jump. Why?

**21**.How are action – reaction forces related in magnitude and direction?

**22**.State the relation between the momentum of a body and the force acting on it.

**23**.(i) A heavy and a light object have same momentum. Which of these is travelling faster?

(ii) State the law of conservation of momentum. Give examples.

## Short Answer Type questions

**1.**There are three solids made up of aluminium, steel and wood, of the same shape and same volume. Which of them would have highest inertia?

**2**.Two friends on roller – skates are standing 5 m apart facing each other. One of them throws a ball of 2 kg towards the other, who catches it. How will this activity affect the position of the two? Explain your answer.

**3**.Give reason and give the law related to these statements:

(a) It is easier to push an empty box than to push the box full of books.

(b) It is difficult for a fireman to hold a hose which ejects large amount of water with high velocity.

**4**.(a) Name the force that keeps the object moving in a circular path with constant acceleration.

(b) What would happen if this force is absent?

a.Leaves of a tree may get detached if we vigorously shake its branch. Explain.

**5**.It is necessary to run along with the moving bus in the same direction of the bus, while alighting from the bus. Give reasons.

**6**.Which of the following has more inertia? Give reason for your answer:

(i) A bicycle and a train

(ii) A rubber ball and a stone of the size.

(iii) A five rupee coin and a one rupee coin.

(iv) A bicycle or a truck.

**7**.Find the change in momentum of a car weighing 1500 kg when its speed increases from 36 km/h to 72 km/h.

**8**.Two objects A and B of same masses and velocity V and 3 V respectively are in motion.

(a) Which object will have larger momentum?

(b) Give reason to support your answer ‘a’.

**9**.While playing football, the goalkeeper did not get sufficient time to stop a fast ball shot towards him. Why did he hurt his hand while doing so?

**10**.The hand gets hurt while punching a wall. Why?

**11**.(i) Explain why is it difficult for a fireman to hold a hose, which ejects a large amount of water at a high velocity.

(ii) Why action and reaction do not cancel each other?

**12**.From a rifle of mass 4 kg, a bullet of mass 50 g is fired with an initial velocity of 35 ms-1. Calculate the initial recoil velocity of the rifle.

**13.**An object of mass 1 kg travelling in a straight line with a velocity of 10 ms-1 collides with, and sticks to a stationary wooden block of mass 5 kg. Then they both move off together in the same straight line. Calculate the total momentum just before the impact and just after the impact. Also calculate the velocity of the combined object.

**14**.What is the effect force, when it is applied in the following cases?

a)Balloon is pressed from opposite sides.

b)A ball is hit with a bat.

c)Spring is compressed.

**15**.If you are trying to push a heavy box on a horizontal surface, list various forces acting on the box. State the condition under which this box will start sliding on the surface. How will the magnitude of applied force required to move the box change if:

a)Weight of the box is increased?

b)The surface on which the box is placed is made more rough?

**16**.A pile of carom coins is hit with a fast sliding strike. What happens to the carom coins and why?

**17**.A stone released from the top of a tower of height 19.6 m. calculate its final velocity just before touching the ground.

**18.**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:

a)The velocity with which the gun recoils.

b)The force exerted on gunman due to recoil of the gun.

**19.**Define SI unit of force. A force of 2 N acting on a bnody changes its velocity uniformly from 2 m/s to 5 m/s in 10 s. calculate the mass of the body.

Class 9 Maths
Class 9 Science