**CBSE PHYSICS Class IX ASSIGNMENT Forces and Laws of motion)**

- What do you mean by a force?
- Give an example of a balanced force?
- Can force change the shape of an object? Give an example to prove your point?
- Do action and reaction force react in the same direction?
- Why a moving ship does takes longer time as compared to a car when equal breaks are applied?
- Why are passengers through in forward direction when a running bus stops suddenly?
- Why do passengers tend to fall sideways when the bus takes a sharp u turn?
- Why should a passenger hold on to prevent himself from swaying in a turning bus?
- Why do passengers tend to fall back when it starts suddenly?
- Why do passengers jumping out of a rapidly moving bus fall forward with his face downwards, if he does not run forward?
- Why does a passenger jumping out of a rapidly moving bus fall forward with his face downwards?
- Why can dust be removed by shaking it, or beating it by a carpet?
- Why does a bullet when fired against a glass window pane make a hole in it, and the glass pane will smash it?
- Why does an athlete take a longer jump if he comes running from a distance than when he jumps suddenly from the take-off line?
- What happens when you shake a wet piece of cloth? Explain, why?
- Why is it advised to tie a rope on the luggage while you travel by the bus?
- How does a boat move forward into the water when the boatman presses one end of the pole against the ground?
- Why is it difficult for a fireman to hose, which ejects large amount of water at a high velocity?
- How much force is needed to accelerate a trolley of mass 20g through 1 m/s2?
- A force of 100N acts on a mass of 25 kg for 5 s .What velocity does it generate?
- A bullet leaves a rifle with a velocity of 100m/s and the rifle of mass 2.5 kg recoils with a velocity of 1m/s. Find the mass of the bullet?
- A certain force acting on a mass of 15kg for 3s, gives it a velocity of 2m/s. Find the magnitude of force?
- A cricket ball of mass 0.15 kg is moving with a velocity of 1.2m/s . Find the impulse on the ball and average force applied by the player if he is able to stop the ball in 0.18s?
- A motor car of mass 200kg is moving with a certain velocity . It is brought to rest by the application of brakes, within a distance o f 20m when the average resistance being offered to it is 500N.What was the velocity of the motor car?
- A body of mass 0.5kg undergoes a change of velocity of 4cm/s in 4s What is the force acting on it?
- A force of 8N acting on an 8kg mass for 4s provides its some velocity. Calculate the velocity?
- What would be the weight of a body of mass 50kg on the surface of the moon, where g = 1.6m/s2 what would be its mass?
- . A boy jumps a distance of 2m on the surface of the earth. What distance will he jump on the surface of the moon where g is 1/6th of the value on the surface of the earth?
- Two bodies of mass 1kg and 2 kg moving in the direction opposite to each other with a speed 5m/s collide. Calculate the total momentum of the system before collision?
- A bullet of mass 15g leaves the barrel of a gun with a velocity of 120m/s.The gun recoils with a velocity of 1m/s. Find the mass of the gun?
- A force of 3N acts on a mass of 0.5kg at rest for 10s. Find the final velocity and the momentum of the body after 10s?
- A force of 80N acting on a certain mass for 3s gives it a velocity of 6m/s. find the mass of the body if the body was initially at rest?
- A toy of mass 0.1kg acquires a speed of 5 m/s when pushed forward. Ahat is the impulse given to the toy?
- A projectile weighing 200kg is fired from a gun with a velocity of 500m/s. If the velocity of recoil of the gun is 12.5m/s calculate the mass of the gun?
- A car of mass 2500kg accelerates at the rate of 4m/s2 and then at the rate of 16 m/s2. Calculate t6he ratio of the forces exerted by the engine in the two cases?

A driver accelerates his car first at the rate of 1.8m/s2 and then at the rate of 1.2m/s2 calculate the ration of the forces exerted by the engines? - A body of mass 5 kg undergoes a change in speed from 30 to 40m/s . calculate its increase in momentum?
- A body of mass 100g is moving with a velocity of 15m/s Find the momentum associated with the ball?
- body of mass 5 kg is moving with a uniform velocity of 10m/s It is acted upon by a force of 20N What will be its velocity after 1s?

- In order to gain a velocity of 12m/s how long should a force of 30N be exerted on a body of mass 5kg?
- The velocity of a body of mass 5kg reduces from 10 m/s to 5 m/s. What is the change in momentum of the body?
- A 5 kg rifle fires a 10g bullet at a velocity of 500m/s find the recoil velocity of the rifle?
- A block of mass 3kg has a velocity of um/s. When a force of 18N acts on the block, it reduces the velocity from U to U/2 after the block has covered a distance of 9 m. Find U?

## 7 comments:

Nice post to practice

can you please post the answers or write the blog from where you found the answers

read other post of this chapter:

Write the questions number you need answer

sir I need answers of question no 21 to question no 36.thank you sir for replying

sir and i need them before sunday evening

21. A bullet leaves a rifle with a velocity of 100m/s and the rifle of mass 2.5 kg recoils with a velocity of 1m/s. Find the mass of the bullet?

Ans: According to law of conservation of momentum = m1u1 + m2u2 = m1v1 + m2v2

0=2.5x1 +m2 x100

2.5/100= the mass of the bullet

25gm= the mass of the bullet

36.A body of mass 5 kg undergoes a change in speed from 30 to 40m/s . Calculate its increase in momentum?

Ans: Increase in momentum =m(v-u) =5 kg(40-30)m/s=50kgm/s

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