Physics

Force and Laws of Motion

Question:

Define force.

Answer:

Force is an external effort in the form of pushing, pulling, stretching, compressing etc.which may move a body at rest or stop a moving body or change the direction of motion of the body or change the size and shape of the body.
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Force and Laws of Motion

Q 1.

What is the total momentum of a bullet and a gun before firing?

Q 2.

Why does a person in a bus tend to fall forward when it stops suddenly ?

Q 3.

A force of 5 N changes the velocity of a body from 10ms-1 to 20ms-1 in 5 sec.How much force is required to bring about the same change in 2 sec ?

Q 4.

Can balanced forces change the shape and size of an object?

Q 5.

Can balanced forces change the shape and size of a body ?

Q 6.

In the above question, which body is damaged more ?

Q 7.

Give atleast four applications of Newton’s second law of motion.

Q 8.

A force of 4 N acts on a body of mass 2 kg for 4 s.Assuming the body to be initially at rest,find (a) its velocity when the force stops acting (b) the distance covered in 10 s after the force starts acting.

Q 9.

What is the SI unit of momentum ?

Q 10.

State Newton’s third law of motion and principle of conservation of momentum.

Q 11.

Explain the use of seat belts in cars.

Q 12.

How Newton's Second law of motion is different from First law?

Q 13.

Fill in the blanks :
The velocity with which gun moves in the backward direction is known as the ______ velocity.

Q 14.

State Newton's third law of motion.

Q 15.

What is the SI unit of impulse.

Q 16.

A machine gun fires 25 g bullets at the rate of 600 bullets per minute with a speed of 200 m/s.Calculate the force required to keep the gun in position.

Q 17.

Two hockey players of opposite teams,while trying to.hit a hockey ball on the ground collide and immediately become entangled.One has a mass of 60 kg,and was moving with a velocity 5.0 m/s,while the other has a mass of 55 kg and was moving faster with a velocity of 6.0 m/s towards the first player,In which direction and with what velocity will they move after they become entangled ? Assume that the frictional force acting between the feet of the two players and ground is negligible.

Q 18.

Define intertia.

Q 19.

Define 1N (Newton).

Q 20.

A 8000 kg engine pulls a train of 5 wagons, each of 2000 kg, along a horizontal track. If the engine exerts a force of 40000 N and the track offers a friction force of 5000 N, then calculate:
(a) the net accelerating force;
(b) the acceleration of the train; and
(c) the force of wagon 1 on wagon 2.

Q 21.

Fill in the blanks :
________ is the tendency of an object to resist a change in motion.

Q 22.

A man pushes a box of mass 50 kg with a force of 80 N.What will be the acceleration of the box ? What would be the acceleration if the mass were halved ?

Q 23.

A bullet of mass 50 g is fired from a gun of mass 6 kg with a velocity of 400 m/s.Calculate the recoil velocity of the gun.

Q 24.

What are balanced forces ?

Q 25.

Can balanced forces stop a moving body ?

Q 26.

What is the other name for Newton's first law of motion ?

Q 27.

When a branch of a tree is shaken, some of the fruits may fall down.Why ?

Q 28.

Is momentum a scalar or vector ?

Q 29.

State and explain Newton’s third law of motion.How will you prove it experimentally ?

Q 30.

Which is having higher value of momentum ? A bullet of mass 10 g moving with a velocity of 400 m/s or a cricket ball of mass 400 g thrown with the speed of 90 km/hr.

Q 31.

An object experiences a net zero external unbalanced force. Is it possible for the object to be travelling with a non-zero velocity? If yes, state the conditions that must be placed on the magnitude and direction of the velocity. If no, provide a reason.

Q 32.

A truck starts from rest and rolls down a hill with a constant acceleration. It travels a distance of 400 m in 20 s. Find its acceleration. Find the force acting on it if its mass is 7 metric tonnes. (Hint: 1 metric tonne = 1000 kg.)

Q 33.

A hammer of mass 500 g, moving at 50 m/s, strikes a nail. The nail stops the hammer in a very short time of 0.01 s. What is the force of the nail on the hammer ?

Q 34.

State Law of conservation of momentum.

Q 35.

A bullet of mass 10 g travelling horizontally with a velocity of 150 m/s strikes a stationary wooden block and comes to rest in 0.03 s. Calculate the distance of penetration of the bullet into the block. Also calculate the magnitude of the force exerted by the wooden block on the bullet.

Q 36.

Fill in the blanks :
Which has more inertia of Cricket ball or a rubber ball of the same size? __________

Q 37.

Fill in the blanks :
When a passenger jumps out of moving bus, he falls down. It is due to _______________.

Q 38.

Fill in the blanks :
A cyclist on a levelled road does not come to rest immediately even he stops pedalling. It is due to ______________.

Q 39.

Which law of motion gives the measure of force?

Q 40.

Do balanced forces cause any change of state of an object?

Q 41.

What do you mean by a resultant force?

Q 42.

Which principle is involved in the working of a jet plane?

Q 43.

What would be the force required to produce an acceleration of 2 m/s2 in a body of mass 12 kg ? What would be the acceleration if the force were doubled ?

Q 44.

For how long should a force of 100 N act on a body of mass 20 kg so that it acquires a velocity of 100 m/s ?

Q 45.

A 150 g ball travelling at 30 m/s strikes the palm of a player’s hand and is stopped in 0 06 sec. Calculate the force exerted by the ball on the hand.

Q 46.

A bullet of mass 20 gram moving with a velocity of 300 m/s gets embedded in a freely suspended wooden block of mass 880 gram.What is the velocity acquired by the block ?

Q 47.

A stone of 1 kg is thrown with a velocity if 20 ms-1 across the frozen surface of a lake and comes to rest after travelling a distance of 50 m.What is the force of friction between the stone and the ice ?

Q 48.

A hockey ball of mass 200 g travelling at 10 m/s is struck by a hockey stick so as to return it along its original path with a velocity of 5 m/s.Calculate the change in momentum of the hockey ball by the force applied by the hockey stick.

Q 49.

A bullet of mass 10 g travelling horizontally with a velocity of 150ms-1 strikes a block and comes to rest in 0.03 s. Calculate the distance of penetration of the bullet into the block.Also, calculate the magnitude of the force exerted by the wooden block on the bullet.

Q 50.

On what factor does inertia of a body depend ?