MCQ Questions for Class 9 Physics Force And Laws Of Motion Quiz 8

Vehicles are provided with shock absorbers. Which of the following laws of Newton given below explain this?

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The first law of motion
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The second law of motion
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The third law of motion
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All of the above

Explanation

The vehicle receives a sudden sharp movement when it moves on uneven surfaces. So, the vehicle receives impulsive force. Using the second law of motion to minimize this impact, shock absorbers are used.

$Impulse=F(Δt)$ (where

$F$ = force and

$\Delta t$ = small change in time)

$F\propto \dfrac {1}{\Delta t}$

The shock absorbers increase the time of sudden sharp movement by reducing impulsive force.

This minimizes the damage. to the vehicle.

Which of the following statements is NOT true?

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When the mass of a body is doubled, the momentum of a body is halved, provided the velocity remains the same.
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The pain we feel in the hand on hitting the wall is a consequence of Newton's third law of motion.
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A table-cloth which is pulled from a table without dislodging the dishes is due to inertia of rest.
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Momentum is a vector quantity.

Explanation

The momentum of a body is a product of mass and its velocity. ie

$\vec P=m\ \vec v$ it is a vector quantity.

hence when the mass of body is doubled by keeping its velocity constant then momentum of body will be double.

hence Statement

$a$ is wrong and statment

$d$ is right.

According to statement given in

$b$ is correct because according to newton's 3rd law; every action have equal and opposite reaction therefore when you will hit the wall by a force (action force), with same force wall will hit your hand (Reaction force) hence hand feel pain.

Statment

$c$ can be explained by the properties of inertia of rest. When you pull the table cloth quickly then external force will not transfer to the dishes so it wil stay in rest.

Two bodies of masses 1m and 4m have the same KE. What is the ratio of their momenta?

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2:1
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1:2
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1:4
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4:1

Explanation

The relation between kinetic energy

$(K)$ and momentum

$(p)$ is given by,

$K=\dfrac{p^2}{2m}$ where

$m$ be the mass of the body

So,

$p=\sqrt{2mK}$

Hence,

$\dfrac{p_1}{p_2}=\dfrac{\sqrt{2(m)K_1}}{\sqrt{2(4m)K_2}}=\sqrt{(1/4)}=2/1$ as they have same kinetic energies so

$K_1/K_2=1$

A 10 N force applied on a body produces in it an acceleration of

$2 \,m\, s^{-2}$ , then the mass of the body is ______.

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10 kg
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2 kg
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5 kg
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6 kg

Explanation

$F=10N$

$a=2m/s^{2}$

By newton second law

$F=ma$

$10=2M$

$M=5Kg$

Which of the following safety features are used in vehicles to reduce the negative effects of inertia?

(i)Safety seat belts
(ii)Automatic air bags
(iii)Absorber bumpers

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Only (i) and (ii)
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Only (ii) and (iii)
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Only (i) and (iii)
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(i), (ii) and (iii)

Explanation

$Force=mass \times \dfrac{momentum}{time}$

since the effect of inertia depend on force if the time of impact is increased and hence the same force will produce less effect of inertia the safety seat belt,automatic air bag,Absorber bumpers produce the same effect to decrease the negative effect of inertia.

A man weighing 60 kg is walking with a uniform velocity of 4 m

$s^{-1}$ . Calculate the momentum of a man.

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120 m $s^{-1}$
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240 m $s^{-1}$
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360 m $s^{-1}$
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480 m $s^{-1}$

Explanation

Given,

$m=60\ kg\\v=4\ m/s$

Momentum = mass

$\times$ velocity.

Momentum of man

$p=m\times v=60\times 4=240\ kg m/s$

Identify the type of force in diagram

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Push
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Pull
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No force is acting
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Both A and B

A man squatting on the ground gets straight up and stand. The force of reaction of ground on the man during the process is

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constant and equal to mg in magnitude
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constant and greater than mg in magnitude.
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variable but always greater than mg
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at first greater than $mg$ , and later becomes equal to $mg$ .

Explanation

When the man gets straight up and stand in this process initially for the man to move upward he needs a net external force in the upward direction which can only be provided by the normal reaction(

$N$ ) from the ground.

Therefore,

$N-mg>0\quad \Rightarrow N>mg$ (initially)

and later when he stands up and becomes static then

$N=mg$

On a stationary sail boat, air is blown from a fan attached to the boat. The boat

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moves in opposite direction in which the air is blown
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does not move
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moves in the same direction in which air blows
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spins around

Select the correct option\options:

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When a body exerts a force on any other body, the second body also exerts an equal and opposite force on the first.
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Forces in nature always occurs in pairs. A single isolated force is not possible
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Any agent, applying a force also experiences a force of equal magnitude but in opposite direction. The force applied by the agent is called Action and the counter force experienced by it is called Reaction.
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None of these

If set of forces acting on a body are balanced, the body

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must be moving
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must be at rest
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must not be revolving
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must not be accelerating

When a bus suddenly takes a turn, the passengers are thrown outwards because of

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Inertia of motion
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Acceleration of motion
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Speed of motion
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Both (b) and (c)

A car accelerates on a horizontal road due to the force exerted by

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The engine of the car
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The driver of the car
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The car on earth
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The road on the car

What causes a moving body to resist a change in its state of motion?

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Its acceleration
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Its speed
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Its inertia
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Its weight

The net force acting is not zero on

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a retarding train
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a ball falling with terminal velocity
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a kite held stationary
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a truck moving with constant velocity
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a book placed on a table

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

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Unable to change by itself the state of uniform motion
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Unable to change by itself the state of rest and or uniform linear motion
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Unable to change by itself the state of rest
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Unable to change by itself the direction if motion

The propulsion of rocket illustrates that :

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Linear momentum is conserved
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Newton's third law is not applicable
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Newton's third law is applicable
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Linear momentum is not conserved

A bowling ball hits a pin as shown, where

$F_{BP}$ represents the force applied by the ball on the pin. Which arrow shows

$F_{PB}$ (force applied by the pin on the ball) correctly?

Explanation

From the third law of motion,

$F_{PB}$ (reaction) is always equal and acts in the opposite direction to

$F_{BP}$ (action).

Fill in the blank:

Tendency of an object to _____ a change in its state of rest or motion is called inertia

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Allow
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Assist
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Resist
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None of these

A bullet is fired from a rifle with a velocity of

$1000\,m/s$ . Its momentum is

$20\ kg\ m/s$ . What will be its mass?

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$10\ g$
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$20\ g$
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$50\ g$
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$100\ g$

Explanation

Given

$:$

Momentum

$=20\,kg\,m/s$

Velocity

$=1000m/s$

We know

$,$

$Momentum = mass \times velocity$

$\begin{array}{l} 20\, kg\, m/s=mass\times 1000\, m/s \\ mass=\dfrac{20}{1000}\ kg=\dfrac { { 20\times 1000} }{ { 1000 } } g=20g \end{array}$

Hence,

option

$(B)$ is correct answer.

Why does an athlete take a run before doing a long jump?

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To cheer the crowd
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She/he likes running
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To gain momentum
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To reduce momentum

$4$ balls are moving in the directions shown. The magnitudes of their momentum are also given in the figure. Find which two have the same momentum.

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$A$ and $B$
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$C$ and $D$
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$A$ and $C$
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$A$ and $D$

The symbol and formula for momentum is

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$m, pv$
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$p, ma$
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$p, mv$
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$M, mv$

Explanation

The momentum, (symbol

$p$ ) of an object is defined as the product of its mass,

$m$ and velocity,

$v.$

i.e.

$p = mv$

There are

$3$ balls of same shape and size made of wood, iron and plastic. Which one of them would have highest inertia?

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Wood
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Iron
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Plastic
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None of these

Explanation

Inertia depends on mass. Higher the mass, higher the inertia. Iron is the heaviest among all

$3$ balls. So it has the highest inertia.

The $SI$ units of Force are _____ or _____.

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$kg \ m/s,\ N$
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$kg\ m/s^2, \ Ne$
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$kg\ km/hr$ , Newton
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$kg\ m/s^2, \ N$

Explanation

$F = ma$ ,

So the

$SI$ unit of force =

$(SI\ \text{unit of }\ m).(SI \ \text{unit of}\ a) = kg \ m/s^2$ or Newton

$(N)$

Choose the correct option.

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Balanced forces do not have any impact on a body
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Balanced force can change shape of an object
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Unbalanced force do not produce motion
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None

If given is the direction of acceleration, where should the direction of force be?

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None of these

Which one of these is a real life application of the third law of motion?

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Working of pulleys
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Use of airbags in cars for safety
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Helicopters creating lift by pushing air down
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Cricketers pulling their hands down while taking a catch

The acceleration of a body depends on:

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The external force acting on the body only
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The mass of the body only
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Both the external force and the mass
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The displacement of the body only

Explanation

$\text{Acceleration}=\dfrac{\text{External net force}}{\text{mass of the body}}$

So, the acceleration depends on both the external force and the mass.

Note: If the motion is uniform acceleration(general case) then the displacement depends on acceleration not vice-versa.

Option C is correct.

A nail driven into a wall by striking it with hammer is an example for

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Force
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Impulse
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acceleration
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mass

CBSE Questions for Class 9 Physics Force And Laws Of Motion Quiz 8 - 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 8 - MCQExams.com

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Practice Class 9 Physics Quiz Questions and Answers

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