sometimes a scalar and sometimes a vector

MCQ Questions for Class 11 Engineering Physics Laws Of Motion Quiz 2

A body of mass M collides with a wall with velocity V and rebounds with the same speed. Its change in momentum is equal to :

0%
Zero
0%
MV
0%
2MV
0%
3MV

Explanation

$\Delta P={ P }_{ 1 }-{ P }_{ 2 }$

$[$ change in momentum

$]$

$=MV-(-MV)\\ \quad \quad \quad =-2MV$

negative sign denotes direction.

Hence option C is correct.

Momentum is defined as :

0%
weight
0%
mass
0%
mass $\times$ velocity
0%
velocity

Galilee's law of inertia is another name for newton's (... ) law of motion.

0%
First
0%
Second
0%
Third
0%
Anyone of the above

A ball of mass

$\dfrac{1}{10}$ kg is thrown against a wall. It strikes the wall normally with a velocity of

$\displaystyle 30{ ms }^{ -1 }$ and rebounds from there with a velocity

$\displaystyle 20{ ms }^{ -1 }$ . The impulse of the force exerted by the ball on the wall is

0%
0.5Ns
0%
50Ns
0%
5 Ns
0%
1Ns

Explanation

Impulse = force x time
= change in momentum

$= mv - mu =0.1(-20-30) =-5$

Since units in all the options are same, we need not bother to think about the units. Also since there is no fight of plus or minus sign in the options, we will give the correct answer as 5 Ns. Note that the direction of initial velocity is considered as positive and that of the final velocity is considered as negative

A cannon after firing recoils due to

0%
Conservation of energy
0%
Backward thrust of gases produced
0%
Newton's first law of motion
0%
Newton's third law of motion

Explanation

Correct Option is D.

Explanation for the correct:

$\bullet$ Newton's Third Law of Motion states that to every Action there is equal and opposite Reaction. Thus firing of bullet from cannon is an Action and there is opposite Reaction on the cannon due to which it recoils. Option D is correct.

$\bullet$ Conservation of Energy states that Energy can neither be created nor destroyed. It can only change it forms.

$\bullet$ Backward thrust of gases is not a Law. It is also one of the consequences of Third Law of Motion.

$\bullet$ First Law of Motion states that if a body is at rest/motion it will continue to remain at rest/motion until any external force is applied.

Thus, Only Option D is correct.

$Force\times time =$ ________. Fill in the blank.

0%
Acceleration
0%
Impulse
0%
Velocity
0%
Momentum

Explanation

Impulse acting on the body is defines as the product of force acting on the body and the time interval for which force has been applied.

$\therefore$ Impulse

$I = F\Delta t$

kg ms

$^{-1}$ is the SI unit of

0%
impulse
0%
force
0%
angular velocity
0%
none of these

Explanation

Impulse

$(I)$ imparted to the body is equal to the change in linear momentum

$(\Delta p)$ of the body.

Impulse

$I = \Delta p$

Thus momentum has the same units as that of impulse.

Since momentum has SI unit as

$kg \ m/s$ , thus impulse also has SI unit as

$kg \ m/s$ .

Impulse is

0%
a scalar quantity
0%
a vector quantity
0%
neither a scalar nor a vector
0%
sometimes a scalar and sometimes a vector

Explanation

Explanation:

$\bullet$ Impulse is change in momentum. So, it is a difference between the final momentum and initial momentum.

$\bullet$ Momentum is vector quantity that has both magnitude and direction. So, the impulse will also have both magnitude and direction. So, impulse is vector quantity.

$Answer:$

Hence, option B is the correct answer.

Column A	Column B
a) Force	i) $f\times t$
b) Momentum	ii) $m\times a$
c) Impulse	iii) $m\times v$

0%
$a - iii, b - ii, c - i$
0%
$a - ii, b - iii, c - i$
0%
$a - i, b - ii, c - iii$
0%
$a - iii, b - i, c - ii$

Explanation

(a) From Newton's second law, Force

$f = m\times a$

(b) Momentum

$P = m\times v$

$I = f\times t$

Choose the wrong statement:

0%
1 kg wt = 9.8 N
0%
Momentum is a vector quantity.
0%
Force is always conserved.
0%
Momentum is conserved in the absence of an external force.

Explanation

$1kg-wt = 1 \times 9.8 N$

$momentum = mass \times velocity$ As velocity is vector, momentum is vector.

Friction is non conservative force.

According to Newton's second law, rate of change of momentum is directly proportional to applied force.

So,if force is zero, momentum is conserved.

So wrong statement is option C.

Two similar trucks are moving with the same velocity on the road. One is loaded and the other is empty. Which truck will require more force to be stopped?

0%
Loaded truck
0%
Empty truck
0%
Both equal
0%
Can't be predicted

Explanation

Force required

$|F| = \dfrac{|\Delta P|}{\Delta t} = \dfrac{|m(0-u)|}{\Delta t} = \dfrac{mu}{\Delta t}$

$\implies$

$|F| \propto m$

$(\because u,\Delta t = constants)$

As the loaded truck has more mass compared to the empty one, thus more force is required to stop the loaded truck.

A body can change its state of rest or of uniform motion on its own. True or false.

0%
True
0%
False

A number of discs, each of momentum

$M kg {m}/{s}$ are striking a wall at the rate of

$n$ discs per minute. The force associated with these discs, in newtons, would be

0%
$\displaystyle\frac{Mn}{60}$
0%
$60 Mn$
0%
$\displaystyle\frac{M}{60n}$
0%
$\displaystyle\frac{n}{60M}$

Explanation

The force is

$F=\dfrac{\Delta P}{dt}$

$momentum=M kg.m/s$

change in time=rate of dics striking wall

$\Delta t=\dfrac{1}{n/minute}=\dfrac{60}{n}$

$F=\dfrac{\Delta P}{dt}=\dfrac{M}{60/n}=\dfrac{Mn}{60}N$

"Every action has its equal and opposite reaction" is Newton's:

0%
First law of motion
0%
Second law of motion
0%
Third law of motion
0%
Fourth law of motion

Explanation

Newton's third law of motion states that every action has an equal and opposite reaction. Force on a body 2 applied by the body 1

$(F_{21})$ is equal and opposite to the force on body 1 applied by the body 2

$(F_{12})$ , i.e.

$F_{21}=-F_{12}$

A long-jumper runs before jumping because

0%
He covers a greater distance
0%
He maintains momentum conservation
0%
He gains energy by running
0%
He gains momentum

The force acting on an object are balanced, then the object:

0%
must be at rest
0%
must be moving
0%
must not be accelerating
0%
must lose energy

Explanation

Balanced forces always result in a zero external force acting on an object i.e

$F_{ext} =0$

$\therefore$ Acceleration

$a = \dfrac{F_{ext}}{m} = 0$

Thus the object must not be accelerating or it must be moving with constant velocity or remain at rest (if it was at rest initially). Hence option C is correct.

An astronaut in space throws an object away from his space shuttle. Which of the following statements is true?

0%
The initial velocity of the astronaut is equal and opposite to the velocity of the tool.
0%
The impulse applied to the astronaut is equal and opposite to the impulse applied to the tool.
0%
The mass of the astronaut is equal to the mass of the tool.
0%
The momentum of the astronaut is greater than the momentum of the tool.
0%
The force applied to the tool is greater than the force applied to the astronaut.

Explanation

From Newton's third law of motion, a reaction force acts on the astronaut equal in magnitude and opposite in direction to the force acted on the object.
Since they would take same amount of time to acts,

$\int Fdt=\int Rdt$

$\implies I_1=I_2$

Hence impulses on both are same in magnitude and opposite in direction.

A simple pendulum, composed of a bob of mass

$m$ connected to the end of a massless rod, executes simple harmonic motion as it swings through small angles of oscillation.The maximum angular displacement with the vertical is denoted by

${ \theta }_{ max }$ . Frictional effects and variation of acceleration due to gravity are negligible.
Find out the correct statement?

0%
At $\theta=0$ , the tangential acceleration is $0$
0%
At $\theta={\theta}_{max}$ , the tangential acceleration is $0$
0%
At $\theta=0$ , the speed is $0$
0%
At $\theta=0$ , the restoring force is maximized
0%
At $\theta={\theta}_{max}$ , the speed is maximized

Explanation

We know the tangential acceleration in SHM is given by

$a=-{\omega}^{2}A\sin{\theta}$

where

$A=amplitude$

therefore at

$\theta=0$

$a=-{\omega}^{2}A\sin{0^0}$

$a=0$ because

$\sin{0^0}=0$

A physics student is performing a experiment in which she twirls rubber stopper at the end of a string around in a circle at nearly constant speed and tries to determine its acceleration. Which of the following single changes would enables her to most nearly double the acceleration of the rubber stopper?

0%
Double the speed of the rubber stopper.
0%
Use a string that is twice as long as the original string.
0%
Reduce the speed of the rubber stopper to half its original value.
0%
Use a string that is half as long as the original string
0%
Use a rubber stopper with twice as much mass as the original rubber stopper.

Explanation

Due to constant speed , student is doing uniform circular motion so tangential acceleration is zero .

as the tangential acceleration is zero , therefore total acceleration will be equal to centripetal acceleration , which is

$a=v^{2}/r$

which can be doubled by using a string that is half as long as the original string .

$a'=\dfrac{v^{2}}{\frac{r}{2}}=2a$

A ride in an amusement park called scream machine swings the riders around a complete vertical circle during the course of the ride.
Identify where on ride rider feels the maximum speed?

0%
Point A
0%
Point B
0%
Point C
0%
Point D
0%
Point E

Explanation

At the lowermost position of the circular motion, the potential energy is zero and thus the kinetic energy of the rider is maximum at that position.

Using

$K.E = \dfrac{1}{2}mv^2$

Hence the rider feels maximum speed at the lowermost position of motion i.e point A.

A ball of mass

$m$ is attached with the string of length

$R$ , rotating in a circular motion, with instantaneous velocity

$v$ and centripetal acceleration

$a$ .
Calculate the centripetal acceleration of the ball if its mass is doubled?

0%
${a}/{4}$
0%
${a}/{2}$
0%
$a$
0%
$2a$
0%
$4a$

Explanation

As centripetal acceleration is given by

$a=v^{2}/R$

therefore centripetal acceleration does not depend upon mass of ball, so it will remain constant ,equal to

$a$ .

Which of the following quantities has equivalent units as Impulse?

0%
Displacement
0%
Velocity
0%
Acceleration
0%
Linear momentum
0%
Kinetic energy

Explanation

Impulse

$I= Fdt=m\frac{dv}{dt} dt=mdv=$ change in linear momentum.

Thus, the linear momentum has equivalent units as Impulse.

A man in a minivan rounds a circular turn at a constant speed. Which of the following would cause the minivan to experience less acceleration ?

0%
traveling faster
0%
traveling around a turn with a smaller circular radius
0%
traveling with more weight in the van
0%
traveling around a turn with a greater circular radius
0%
traveling the opposite direction around the same turn

Explanation

$a=\frac { { v }^{ 2 } }{ R }$ . So for the lesser acceleration the speed of the car should be less and the radius of curvature must be large. Correct answer is option D

A simple pendulum, composed of a bob of mass

$m$ connected to the end of a massless rod, executes simple harmonic motion as it swings through small angles of oscillation.The maximum angular displacement with the vertical is denoted by

${ \theta }_{ max }$ . Frictional effects and variation of acceleration due to gravity are negligible.
Which one of the following would enable you to calculate the length of the pendulum?

0%
The mass of the bob
0%
The period of the oscillations
0%
The tangential acceleration at $\theta = 0$
0%
The maximum speed of the bob
0%
The acceleration at $\theta = {\theta}_{max}$

Explanation

For the small oscillation, the motion of the pendulum can be treat as a simple harmonic motion. So, time period of a SHM is

$T=2\pi\sqrt{\frac{l}{g}}$

Thus, time period would enable you to calculate the length of the pendulum.

The amateur boxers, use larger and more padded gloves than professional boxers. The amateur boxers are more protected from injury because:

0%
The larger glove exerts a larger impulse on the boxer
0%
The larger glove exerts a larger force on the boxer
0%
The larger glove exerts more energy on the boxer
0%
The larger glove increases time of impact on the boxer
0%
The larger glove increases the power exerted on the boxer

Explanation

We have impulse

$\vec{I}=\vec{F}\times t=\vec{p}_{2}-\vec{p}_{1}$

when a boxer hits another boxer , change in momentum remains constant therefore product of force and time should be constant .we can decrease the force by increasing time of impact so boxer uses larger gloves to increase the time of impact thus decreases the force and avoids from injury.

A force acts on a body of mass 3 kg such that its velocity changes from 4 m

$s^{-1}$ to 10 m

$s^{-1}$ .Calculate the change in the momentum of the body.

0%
2 kg m $s^{-1}$
0%
14 kg m $s^{-1}$
0%
18 kg m $s^{-1}$
0%
42 kg m $s^{-1}$

Explanation

A force acts on a body of mass 3 kg such that its velocity changes from 4 m/s to 10 m/s

change in momentum

$\Delta p=m(v_1-v_2)=3*(10-4)=18kg m/s$

Which of the following balls is easier to catch even though all of them are moving with the same velocity?

0%
Tennis ball
0%
Cricket ball
0%
Basket ball
0%
Both cricket and basket ball

Which of the following statements is NOT true?

0%
When the mass of a body is doubled, the momentum of a body is halved, provided the velocity remains the same.
0%
The pain we feel in the hand on hitting the wall is a consequence of Newton's third law of motion.
0%
A table-cloth which is pulled from a table without dislodging the dishes is due to inertia of rest.
0%
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.

Maximum safe speed does not depend upon

0%
radius of curvature
0%
angle of inclination with the horizontal
0%
mass of the vehicle
0%
acceleration due to gravity

Explanation

Formula for maximum safe speed is

$v = \sqrt {\dfrac {rg (\mu + tan\theta)}{1 - \mu \tan\theta}}$

r is radius of curvature

g is acceleration due to gravity

$\mu$ is coefficient of friction

$\theta$ is angle of banking

So, it is independent of mass. Option C is correct.

Which of the following physical quantities has the same units as that of impulse?

0%
Momentum
0%
Force
0%
Torque
0%
Couple

State whether true or false.

An increase in the base area leads to the decrease in stability of the object.

0%
True
0%
False

What does the principle of conservation of linear momentum state?

0%
The linear momentum of a system cannot be changed.
0%
The linear momentum of a system cannot remain constant.
0%
The linear momentum of a system can be changed only if internal forces act.
0%
The linear momentum of a system can be changed only if external forces acts on it.

Free body diagrams doesn't play any role in making the calculations on the conditions of the equilibrium of the body.

0%
True
0%
False

The maximum safe speed for a vehicle taking a turn on a curved banked road, does not depend upon

0%
acceleration due to gravity
0%
mass of the vehicle
0%
angle of inclination with the horizontal
0%
radius of curvature of the track

Explanation

The maximum safe speed for a vehicle taking a turn on a curved banked road
is given by

$v=\sqrt{(\mu*rg)}$
hence it doesn't depend upon the mass of vehicles

Which of the following is not force?

0%
Impulse
0%
Tension
0%
Thrust
0%
Weight

Explanation

Tension, trust, weight are all common forces in mechanics whereas impulse is not a force.
Impulse = force

$\times$ Time duration.

Banking of roads is provided at turns to :

0%
reduce intertia
0%
increase centripetal force
0%
increase fiction
0%
none of these

What is the other name of Galileo's law of falling bodies?

0%
Law of motion
0%
Newton's first law
0%
Newton's second law
0%
Newton's third law

The banking angle is independent of

0%
the velocity of the vehicle
0%
mass of the vehicle
0%
the radius of curvature of the road
0%
the height of inclination

Explanation

The banking angle is an angle of vehicle w.r.t. to the road while taking turn on road. is given by

$tan\theta =\dfrac{v^2}{rg}$ So it is independent of mass of Vehicle

A large force is acting on a body for a short time. The impulse imparted is equal to the change in :

0%
Acceleration
0%
Momentum
0%
Energy
0%
Velocity

Explanation

If a large force F acts for a short time dt the impulse imparted I is

$I=Fdt=\dfrac{dp}{dt}dt$

$I=dp$ = change in momentum

Force is directly proportional to

0%
Rate of change in distance
0%
Rate of change in velocity
0%
Momentum
0%
Rate of change in momentum

Explanation

Second law of motion yields

$F = \Delta p/\Delta t$

A cyclist is moving on a circular track of radius

$80\ m$ with a velocity of

$72\ km/hr$ . He has to lean from he vertical approximately through an angle-

0%
$\tan ^{ -1 }{ \left( 1/4 \right) }$
0%
$\tan ^{ -1 }{ \left( 1 \right) }$
0%
$\tan ^{ -1 }{ \left( 1/2 \right) }$
0%
$\tan ^{ -1 }{ \left( 2 \right) }$

Explanation

It is given that,

$v=72Km/hr$

$=\dfrac{5}{18}\times 72=20\,m/s$

$radius\,\,r=80\,m$

Bending of a cyclist in circular motion is given by the relation as

$\tan \theta =\dfrac{{{v}^{2}}}{rg}$

$\tan \theta =\dfrac{20\times 20}{80\times 10}$ $\theta ={{\tan }^{-}}(\dfrac{1}{2})$

A turn of radius 100 m is being designed for a speed of 25 m/s. At what angle should the turn be banked?

0%
32 degrees
0%
60 degrees
0%
45 degrees
0%
10 degrees

Explanation

The angle of banking is given by

$\theta = tan^{-1}(v^2/rg)$ . Substituting the values, we get,

$\theta = tan^{-1}(25^2/100 \times 10)=tan^{-1}(0.625) = 32$ degrees

The correct option is (a)

The symbol and formula for momentum is

0%
$m, pv$
0%
$p, ma$
0%
$p, mv$
0%
$M, mv$

Explanation

The momentum, (symbol

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

$m$ and velocity,

$v.$

i.e.

$p = mv$

What is the difference of force of friction acting on a body moving on a fixed surface?

0%
Along the different of motion
0%
Opposite to the direction of motion
0%
Independent of Motion
0%
Both (A) and (B)

Explanation

When we try to slide a body on a surface, the motion of the body is opposed by a force called the force of friction. The frictional force arises due to intermolecular interaction.

When an external force $(F)$ is applied to move the body and the body does not move, then the frictional force acts opposite to applied force $F$ and is equal to the applied force i.e., $F-f=0$ frictional force , $f$ and applied force $F$ . When the body remains at rest, the frictional force is called the static friction. Static friction is a self-adjusting force.

Friction force, ${{f}_{r}}=\mu mg$

Where,

$\mu$ = coefficient of friction.

Hence, friction force act opposite to the direction of motion.

1059206_1165651_ans_ac318012a5c6453e8458a49ba0fd6d85.png

A brick of mass

$m$ , tied to a rope , is being whirled in a vertical circle, with a uniform speed. The tension in the rope is:

0%
The same throughout
0%
Largest when the brick is at the highest point of the circular path and smallest when it is at the lowest point
0%
Largest when the rope is horizontal and smaller when it is vertical.
0%
Largest when the brick is at the lowest point of the circular path and smallest when it is at the highest point

Explanation

$T_H + mg = m \omega^2 r$

$T_L - mg = m\omega^2 r$

$\therefore T_L > T_H$

1175239_1075462_ans_a1d2e5bc4d054f8a98ea5dd7597336ca.PNG

When the constant force is 10 N for time period 1 s to 10 second then, find the impulse?

0%
45 Ns
0%
50 Ns
0%
90 Ns
0%
100 Ns

Explanation

Constant force, $F=10\,N$

Time period, ${{t}_{2}}=10\,s\,\,and\,{{t}_{1}}=1s$

Impulse, $I=\int{F.dt}=F\int{dt}$ Area of F and t graph.

Where,

$F$ =force

$t$ =time

$I=F({{t}_{2}}-{{t}_{1}})=10(10-1)=90\,Ns$

Hence, impulse is $90\,Ns$

A force of

$10 \,N$ acts on a body of mass

$0.5 \,kg$ for

$0.25 \,sec$ starting from rest. What is its momentum now?

0%
$2.5 \,N/sec$
0%
$0.25 \,N/sec$
0%
$0.5 \,N/sec$
0%
$0.75 \,N/sec$

Explanation

$Ft = mV_2 - mV_1 \Longrightarrow 10 \times 0.25 = P_t - P_i, P_t = 2.5$

Force acting on a body is given by

$F=(1200-4\times 10^{5}t)\ N$ . After starting the motion to it moves with constant velocity, how much impulse of force is acting on it?

0%
Zero
0%
$0.9\ Ns$
0%
$1.8\ Ns$
0%
$3.6\ Ns$

The linear momentum of a body of mass m moving with velocity is :

0%
$v/m$
0%
$m/v$
0%
$mv$
0%
$1/mv$

Explanation

$(c) mv$
Linear momentum can be defined as the product of mass and velocity of an object

What is the unit of momentum?

0%
$kg$ $m/s$
0%
$kg$ $ms$
0%
$kg$ $m/s^{2}$
0%
$m/s$

Explanation

$kg$ $m/s$

$Momentum = mass \times velocity.$

Thus, its S.I. unit is $kg$ $m/s$ .

CBSE Questions for Class 11 Engineering Physics Laws Of Motion Quiz 2 - MCQExams.com

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Practice Class 11 Engineering Physics Quiz Questions and Answers

CBSE Questions for Class 11 Engineering Physics Laws Of Motion Quiz 2 - MCQExams.com

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Practice Class 11 Engineering Physics Quiz Questions and Answers

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