Force and Laws of Motion


Define momentum.


Momentum is defined as the product of its mass and velocity.
i.e. Momentum (P) = mass(m) x velocity(v).

Momentum is a measure of the quantity of motion of a body. It is a vector quantity. It has both direction and magnitude. and its direction is same as the direction of velocity. The SI unit of momentum is kg-m/s.


Force and Laws of Motion

Q 1.

The following is the distance-time table of an object in motion:

Time in seconds       Distance in meters
0 0
1 1
2 8
3 27
4 64
5 125
6 216
7 343

(a) What conclusion can you draw about the acceleration? Is it constant, increasing, decreasing, or zero?
(b) What do you infer about the forces acting on the object?

Q 2.

Why mass is sometimes called coefficient of linear inertia?

Q 3.

Justify Newton's first law gives notion (or definition) about force.

Q 4.

Is Newton's second law of motion is consistent with the first law? How?

Q 5.

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

Q 6.

When two objects act on each other, does action-reaction force pair cancel out each other?

Q 7.

Two objects, each of mass 1.5 kg, are moving in the same straight line but in opposite directions. The velocity of each object is 2.5 m/s before the collision during which they stick together. What will be the velocity of the combined object after collision?

Q 8.

What do you mean by a resultant force?

Q 9.

Define momentum.

Q 10.

What is the SI unit of momentum?

Q 11.

In the following example, try to identify the number of times the velocity of the ball changes:

A football player kicks a football to another player of his team who kicks the football towards the goal. The goalkeeper of the opposite team collects the football and kicks it towards a player of his own team?

Also identify the agent supplying the force in each case.

Q 12.

Why do you fall in the forward direction when a moving bus brakes to a stop and fall backwards when it accelerates from rest?

Q 13.

What are balanced and unbalanced forces?

Q 14.

An object of mass 5 kg is moving with a velocity 4 m/s. A constant force of 20 N acts on the object. What will be the velocity after 3 s.

Q 15.

What is impulse?

Q 16.

The speed-time graph of a car is shown below. The car weighs 1000kg. 
(i) Find the distance covered by the in fits two seconds.
(ii) Find how much force is applied by the car brakes in the fifth second so that the car comes to an halt by sixth second.

Q 17.

Fill in the blanks :
The natural tendency of objects to resist a change in their state of rest or of uniform motion is called ______.

Q 18.

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

Q 19.

Why does a bicycle slow down when the cyclist stop pedalling?

Q 20.

When a force acts on a body, what are the two essential effects it can produce?

Q 21.

What do you mean by an imapct force?

Q 22.

Name the principle on which a rocket works.

Q 23.

When a force acting on a body has equal and opposite reaction, then why should the body move at all?

Q 24.

State why Newton's first law of motion is called law of inertia.

Q 25.

Name the categories of forces based on interaction.

Q 26.

What are non-contact forces? Give examples.

Q 27.

State Newton's third law of motion.

Q 28.

What is collision? What are the types of collision?

Q 29.

Fill in the blanks :
An imaginary co-ordinate system which is either at rest or in uniform and where Newton's laws are valid is called an _______ frame of reference.

Q 30.

Fill in the blanks :
On what factor does the inertia of a body depends? ____________

Q 31.

Give an example that force can make a stationary body move.

Q 32.

A body is moving with uniform acceleration. Is its momentum constant?

Q 33.

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 34.

What are contact forces? Give examples

Q 35.

Suppose a ball of mass m is thrown vertically upward with an initial speed v, its speed decreases continuously till it becomes zero. Thereafter, the ball begins to fall downward and attains the speed v again before striking the ground. It implies that the magnitude of initial and final momentums of the ball are same. Yet, it is not an example of conservation of momentum. Explain why ?

Q 36.

Two persons manage to push a motorcar of mass 1200 kg at a uniform velocity along a level road. The same motorcar can be pushed by three persons to produce an acceleration of 0.2m s-2. With what force does each person push the motorcar?
(Assume that all persons push the motorcar with the same muscular effort.)

Q 37.

Are there any limitations to Newton's Laws of motion?

Q 38.

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

Q 39.

Fill in the blanks :
An umbrella protects us from rain it is based on the property of _____________.

Q 40.

Fill in the blanks :
It is dangerous to jump out of a moving bus because due to _________ one falls forward.

Q 41.

Fill in the blanks :
An athlete often jumps before taking a long jump. It is due to ________________.

Q 42.

Fill in the blanks :
When a hanging carpet is beaten with stick, the dust particles start coming out of it. It is due to ______________.

Q 43.

Fill in the blanks :
The property of an object to resist changes in its rotational state of motion is called ________.

Q 44.

What are balanced forces?

Q 45.

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

Q 46.

If the body is found to be accelerated, is the force acting on it balanced or unbalanced?

Q 47.

If action is always equal to the reaction, explain how a horse can pull a cart.

Q 48.

Law of conservation of momentum is applicable to an isolated system. What do you mean by an isolated system?

Q 49.

Fill in the blanks :
When a car enters a curved path, the person sitting in it is thrown outwards. This is because of the property of ______________.

Q 50.

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