explains the way the force acts on a body

defines the force qualitatively

defines the force quantitatively

MCQ Questions for Class 9 Physics Force And Laws Of Motion Quiz 3

Two bodies A and B of same mass are moving with velocities

$v$ and

$2v$ respectively. What is the ratio of their momentum ?

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3:2
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2:1
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1:2
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1:1

Explanation

(i) Inertia - Inertia depends on mass, And since the mass of the two body is the same, therefore their inertia will be in the ratio of

$1$ :

$1$

(ii) Momentum -

$p = mv$
From, above we see momentum is directly proportional to mass and velocity.
Since mass is equal, in this case velocity with determine the ratio of momentum.
Velocity of body

$A = v$
Velocity of body

$B = 2v$
So. its ratio =

$1$ :

$2$

One Newton is the force, which produces an acceleration of :

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$1 ms^{-2}$ on a body of mass $1 gm$
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$1 cms^{-2}$ on a body of mass $1 kg$
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$1 cms^{-2}$ on a body of mass $1 gm$
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$1 ms^{-2}$ on a body of mass $1 kg$

Explanation

Newton is unit of force in SI system: 1 Newton is the force needed to accelerate 1 kg of mass at the rate of 1

$m/s^2$ .
We know that

$Force = mass \times acceleration$
where S.I unit of mass is

$kg$ and S.I. unit of acceleration is

$m/s^{2}$

$\therefore 1 N = 1 kg \times 1 m/s^{2}$

Can a body moving with a uniform velocity be in equilibrium?

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Yes, since the net force acting on it is zero.
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No, as the acceleration of the body is zero.
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No, as the velocity of the body is constant.
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None of the above.

Which law is the special case of Newton's second law of motion ?

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Newton's third law
0%
Kepler's law
0%
Newton's first law
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Coulombs law.

Explanation

Newton's First Law of Motion states that a body at rest will remain at rest unless an outside force acts on it, and a body in motion at a constant velocity will remain in motion in a straight line unless acted upon by an outside force.

If a body experiences an acceleration ( or deceleration) or a change in direction of motion, it must have an outside force acting on it. Outside forces are sometimes called net forces or unbalanced forces. The property that a body has that resists motion if at rest, or resists speeding or slowing up, if in option, is called inertia. Inertia is proportional to a body's mass, or the amount of matter that a body has. The more mass a body has, the more inertia it has.

The Second Law of Motion states that if an unbalanced force acts on a body, that body will experience acceleration ( or deceleration), that is, a change of speed. One can say that a body at rest is considered to have zero speed, ( a constant speed). So any force that causes a body to move is an unbalanced force. Also, any force, such as friction, or gravity, that causes a body to slow down or speed up, is an unbalanced force. This law can be shown by the following formula $F= ma$

F is the unbalanced force
m is the object's mass
a is the acceleration that the force cause

Which is the Newton's second law of motion ?

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All forces in the universe occur in equal but oppositely directed pairs.
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An object will remain at rest or in uniform motion in a straight line unless acted upon by an external force.
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The rate of charge of linear momentum is equal to force acting on the body.
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None of these.

The SI unit of momentum is :

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$kg ms^{-1}$
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$kg m s^{-2}$
0%
$kg m s^{2}$
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$kg m^{-1}s^{-1}$

A tennis ball and a cricket ball, both are stationary. To start motion in them

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a less force is required for the cricket ball than for the tennis ball
0%
a less force is required for the tennis ball than for the cricket ball
0%
same force is required for both the balls
0%
nothing can be said

A person pushing a wall hard is liable to fall back. Which law is related for this ?

0%
Newton's first law
0%
Newton's second law
0%
Newton's third law
0%
Newton's gravitational law

Explanation

If a person applies a force

$F$ on the wall, wall applies the same force on the person in opposite direction. Since wall is very massive as compared to the person, it doesn't move, but the person is likely to fall back because of the reaction force.

Newton's third law:

0%
defines the force qualitatively
0%
defines the force quantitatively
0%
explains the way the force acts on a body
0%
gives the direction of force

The acceleration produced in a body by a force of given magnitude depends on:

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size of the body
0%
shape of the body
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mass of the body
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none of these

Explanation

Newton's second law of motion,

$F=ma$ , where

$m$ is mass of an object which acquires acceleration

$a$ when force

$F$ is applied on it.
For a force of constant magnitude,

$a\propto{\dfrac{1}{m}}$ i.e. acceleration is inversely proportional to mass.

How does the acceleration (

$a$ ) produced by a given force (

$F$ ) depend on mass (

$m$ ) of the body?

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$F=\dfrac{m}{g}$
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$F=mg$
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$F=ma$
0%
$F=\dfrac{m}{a}$

Explanation

According to Newton's second law of motion,

$F=ma$ , where

$m$ is mass of an object which acquires acceleration

$a$ when force

$F$ is applied on it.
For a constant force,

$a\propto{\dfrac{1}{m}}$

Or, for a given force, acceleration is inversely proportional to the mass of the object.

'The action and reaction are equal in magnitude'. Is this statement true and which law is related with it ?

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Yes, Newton's second law.
0%
Yes, Newton's third law.
0%
No, Newton's third law.
0%
Yes, Newton's first law.

'The action and reaction both act simultaneously.' Is this statement true and what is the net force ?

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yes, zero
0%
no, zero
0%
yes, positive
0%
no, negative

You pull your hands back while catching a fast moving cricket ball. Which law is used to explain it ?

0%
law of inertia.
0%
Newton's second law of motion
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Newton's first law of motion
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Newton's third law of motion

A force of

$10 N$ acts on a body of mass

$5 kg$ . Find the acceleration produced.

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$5$ ${ ms }^{ -2 }$
0%
$50$ ${ ms }^{ -2 }$
0%
$2$ ${ ms }^{ -2 }$
0%
$2.5$ ${ ms }^{ -2 }$

Explanation

F = 10 N, m = 5 kg
Putting the values in

$F=m\times a$

$10=5\times a$

$a=2 m/s^2$

The tendency of a body to resist acceleration is called:

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Force
0%
Retardation
0%
Inertia
0%
mass

What kind of force acting on an object brings it in motion?

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internal
0%
external
0%
null force
0%
None of the above

Which is not the unit of Force?

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Pound
0%
Dyne
0%
Joule
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Newton

Explanation

$\textbf{Hint}$ Apply newton's second law of motion.

STEP (1): SI Unit

Force acting on the body may affect the shape of the body or it will accelerate or decelerate the body, or it will give motion to the static body or it will stop the motion of the dynamic body.

$F = ma$

Where $'F'$ = force applied, $'m'$ = mass and $'a'$ = acceleration

Acceleration $a = \dfrac vt$

Where $v$ = velocity (in m/s)

Here $'m'$ is mass and $'s'$ is seconds

Time $'t'$ is in seconds

Therefore acceleration unit is = $\dfrac{\dfrac ms}s = \dfrac m{s^2}$

Hence unit of force = $kg \dfrac m{s^2} = Newton$ (in S.I. unit) i.e, option $D$ is a unit of force

Newton can converted into Pound

that is 1 Newton = 0.22481 pound ( in FPS system ) i.e, option $A$ is unit of force

$\textbf{Step2:CGS Unit}$

$F = \dfrac{g.cm}{s^2} = Dyne$ (in C.G.S. unit) i.e, option $B$ is a unit of force

Here $'g'$ is grams , $'cm'$ is centimeters and $'s'$ is seconds

Conclusion: Joule is the correct answer because it is the unit of energy.

Action and reaction act on:

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same body in opposite directions
0%
different bodies in opposite directions
0%
different bodies, but in same direction
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same body in same direction

What is an expression for the force due to gravity on a body of mass

$m$ ?

0%
$F=0$
0%
$F=m/g$
0%
$F=g$
0%
$F=mg$

Explanation

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.

This verbal statement can be expressed in equation form as follows:

$a=\dfrac{F}{m}$

put $a=g$ ; gravitational acceleration,

So,

$F=mg$

In Figure, a block of weight

$15 \ N$ is hanging from a rigid support by a string. What force is exerted by
(a) block on the string,
(b) string on the block.

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(a) $15$ $N$ downwards , (b) $15$ $N$ upwards
0%
(a) $15$ $N$ downwards , (b) $15$ $N$ downwards
0%
(a) $15$ $N$ upwards , (b) $15$ $N$ upwards
0%
(a) $15$ $N$ upwards , (b) $15$ $N$ downwards

Explanation

(a) Block has a tendency to fall towards the ground. Therefore, block exerts a downward force on the string which is equal to its weight i.e.

$15 N$ .
(b) Since, system is balanced and motionless, all the forces will be balanced. Due to weight of the block, an equal and opposite tension force is acting on the string. Therefore, string exerts a force of

$15 N$ in the upward direction.

A boy pushes a wall with a force of

$10 N$ towards east. What force is exerted by the wall on the boy?

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$10$ $N$ towards east.
0%
$10$ $N$ towards west.
0%
$10$ $N$ towards north.
0%
$10$ $N$ towards south.

Identify the force which is used to lift an object:

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Horizontal pull
0%
Horizontal push
0%
Vertical Pull
0%
Vertical Push

State whether given statement is True or False.
In the second law,

$F=0$ implies

$a=0$ . The second law is obviously consistent with the first law

0%
True
0%
False

To maintain a body in uniform motion, we need to apply an external force to counter the frictional force

0%
True
0%
False

Acceleration of a body can be zero when

0%
No force is acting on it
0%
One force of infinite magnitude is acting on it
0%
Multiple forces are acting on it
0%
Can never be zero

The earth pulls a stone downwards due to gravity. The stone exerts:

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an equal and opposite force on the earth
0%
a greater force on the earth
0%
a lesser force on the earth
0%
no force on the earth

State whether given statement is True or False.
An experienced cricketer allows a shorter time for his hands to stop the ball so as to catch the ball easily.

0%
True
0%
False

State whether given statement is True or False.
An object moving on a frictionless horizontal surface should move with constant velocity

0%
True
0%
False

It is easy to stop a tennis ball than a cricket ball moving with the same velocity. This is because:

0%
tennis ball has less momentum than cricket ball
0%
tennis ball is soft and offers less friction
0%
cricket ball is hard and offers more friction
0%
none of these

CBSE Questions for Class 9 Physics Force And Laws Of Motion Quiz 3 - MCQExams.com

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Practice Class 9 Physics Quiz Questions and Answers

CBSE Questions for Class 9 Physics Force And Laws Of Motion Quiz 3 - MCQExams.com

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Practice Class 9 Physics Quiz Questions and Answers

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