Important Questions (1 mark): Forces & Laws of Motion


25 Questions MCQ Test NCERT Textbooks (Class 6 to Class 12) | Important Questions (1 mark): Forces & Laws of Motion


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QUESTION: 1

Identify the incorrect statement

Solution:

Weight of the body is the force by which it is attracted by earth.
The spring force is the force exerted by a compressed or stretched spring upon any object that is attached to it. An object that compresses or stretches a spring is always acted upon by a force that restores the object to its rest or equilibrium position. So, the spring force does not always pushes a body.
Frictional force always acts opposite to the surface of contact.

QUESTION: 2

Some of the leaves may get detached from a tree if we vigorously shake its branch because of

Solution:

If a branch of a tree is vigorously shaken, some of the leaves may get detached from tree due to inertia of rest. The leaves tend to remain in rest but branches come in motion.

QUESTION: 3

Essential characteristic of equilibrium is

Solution:

At equilibrium, the acceleration is equal to zero. So, there is no net change in acceleration of the moving body.

QUESTION: 4

“Inflated balloon lying on the surface of a floor moves forward when pierced with a pin. The above mentioned phenomenon is due to

Solution:

Inflated balloon lying on the surface of a floor moves forward when pierced with a pin due to Newton’s third law of motion. The air coming out of the balloon forces the balloon in opposite direction.

QUESTION: 5

A unit of force is

Solution:

The SI unit of force is Newton, which is equal to the mass/ acceleration. 
Newton =Kg/ms2= Kgms−2.

QUESTION: 6

Inertia is the property of a body by virtue of which the body is

Solution:

Inertia is the property of a body by virtue of which the body unable to change the state of rest or state of motion and direction as inertia is the tendency to oppose the change in state or direction.

QUESTION: 7

To every action there is an,

Solution:

To every action, there is an equal and opposite reaction. This is the newton’s third law of motion.

QUESTION: 8

The change in the momentum of a body in 0.01 second is 10 kg ms-1. The force acting on this body is

Solution:

The force acting on a body is equal to rate of change of momentum. Change of momentum = 10 Kg/s, time taken = 0.01 second. Force = 10/0.01 = 1000N.

QUESTION: 9

10dyne is equal to

Solution:

One Newton (1N) is equal to 105 dyne. Both dyne and Newton is unit of force.

QUESTION: 10

Which has more inertia?

Solution:

Inertia of the body is proportional to the mass of the body. 5 Rs coin is heavier than 5 Rs note and 1 Rs coins. So, inertia of 5 Rs coin more than others.

QUESTION: 11

“Forces always occur in pairs”. From which law can we conclude the above statement?

Solution:

The force always occurs in pairs. According to third law of motion, there is equal and opposite reaction. So two force, action and reaction acts in pair always.

QUESTION: 12

Statement A: Rocket can propel its self in vacuum. 
Statement B: Newton’s laws are universal. 
Which of the two statements is true?

Solution:

Rocket moves forward according to newton’s third law of motion. The gas and other substance coming out from the tail push the rocket in forward direction. Newton’s laws are universal.

QUESTION: 13

A force has

Solution:

A force has both magnitude as well as direction. Force is a vector quantity. Force is the product of mass and acceleration.

QUESTION: 14

A high jumper runs for a while before taking high jump so that the inertia of __________ help him in taking a long jump.

Solution:

A high jumper runs for a while before taking high jump so that the inertia of motion help him in taking a long jump. Inertia of motion tends to remain in state of motion.

QUESTION: 15

Frictional force

Solution:

Frictional force always opposes relative motion between the surfaces of contact. The direction of force is always in opposite direction.

QUESTION: 16

A ball is dropped from a height of 10m. Ball is embedded in sand of 1m and stops.

Solution:

When body is dropped from height, the potential energy deceases and kinetic energy increases. A ball dropped from height will conserve only kinetic energy.

QUESTION: 17

Statement A: Gravitational force is the weakest force in nature 
Statement B: Electrostatic force is the example of non – contact force
Which of the above two statement is true?

Solution:

Gravitational force is very weak force as it depends upon mass of the body and distance between two objects. Electrostatic force is non-contact force.

QUESTION: 18

If P and Q are two bodies with masses 10 kg and 5kg respectively, then which body has more inertia?

Solution:

The inertia of the body is proportional to mass of the body. So, body P with masses 10 kg will have more inertia in comparison to body Q of mass 5 kg.

QUESTION: 19

‘Any two forces which are equal and opposite form an action and reaction pair’ The above statement is

Solution:

The two forces acting on same body, which are equal and opposite direction forms action and reaction. This is the newton’s thirds law of motion.

QUESTION: 20

Two bodies of masses 1kg and 5kg are dropped gently from the top of a tower. At a point 50cm from the ground both the bodies will have the same

Solution:

The velocity of the body falling towards depends upon gravitational force acting on it. So, both the body of masses 1 kg and 5 kg will have same velocity at particular height and fall at same time at the ground.

QUESTION: 21

Ayush hits a cricket ball which than rolls of a level ground after covering a short distance, the ball comes to rest. The ball slows to a stop because

Solution:

The ball moving on level ground comes to rest after covering a short distance due to frictional force acting on it. So, ball slows to a stop because there is a force on the ball opposing the motion.

QUESTION: 22

In a football and stone of same size, the inertia of 
A. Football is greater
B. Football is lesser 
C. Stone is greater 
D. Stone is lesser 

Solution:

Inertia is directly proportional to the mass of the body. Higher the mass of the body, the higher will be the inertia.

QUESTION: 23

“Action and reaction are equal and opposite but even then they do not cancel each other” the above statement is

Solution:

Action and reaction are equal and opposite but even they do not cancel each other because they acts in opposite direction. Hence the statement is correct.

QUESTION: 24

Statement A: Calculus, a new branch of mathematics was stated by Newton. 
Statement B: If mass remains same, doubling the force will reduce the acceleration to half. 
Which of the above two statements is true

Solution:

The branch of mathematics, called Calculus was stated by Newton. Force is the product of mass and acceleration. So, acceleration= force /mass. Doubling of force will increase the acceleration if mass is kept same.

QUESTION: 25

Match the following with correct response.

Solution:

As described by the third of Newton's laws of motion of classical mechanics, all forces occur in pairs such that if one object exerts a force on another object, then the second object exerts an equal and opposite reaction force on the first.
Newton's second law of motion can be formally stated as follows: The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object.
Momentum is not a scalar quantity. Momentum is a vector, which means it has a magnitude and a direction. Linear momentum is the product of an object's.
When two forces acting on an object are not equal in size, we say that they are unbalanced forces. The overall force acting on the object is called the resultant force . If the forces are balanced, the resultant force is zero. An object having balanced forces definitely cannot be accelerating. This means that it could be at rest and staying at rest or could be in motion at constant velocity.