MCQ Questions for Class 9 Physics Work And Energy Quiz 6

An overhead tank having some water possesses .......... energy.

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Kinetic
0%
Potential
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Thermal
0%
Electrical

Explanation

We know that Potential energy is the energy possessed by a body by the virtue of its position.

$\therefore$ An overhead tank having some water possesses Potential energy, as it is at a height.

Potential energy is directly proportional to:

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velocity of the body
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speed of the body
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height of the body from the surface
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shape of the body

Which of the following does has kinetic energy ?

0%
An inflated balloon
0%
Water in a flowing river
0%
A fruit on the tree
0%
A stationary plane

Which of the following possesses kinetic energy?

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A fallen tree
0%
Running athlete
0%
Wound watch spring
0%
Boy standing on the road

A box of mass

$1\ kg$ is pulled on a horizontal plane of length

$1\ m$ by a force of

$8\ N$ then it is raised vertically to a height of

$2$ m, the net work done is:

0%
28 J
0%
8 J
0%
18 J
0%
none of the above

Explanation

$W=mgh+FS=1(10)(2)+8\times 1=20+8=28J$

Energy is the capacity to do work.

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True
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False

A rigid body of mass

$m$ kg is lifted uniformly by a man to a height of one metre in

$30$ sec. Another man lifts the same mass to the same height in

$60$ sec. The work done on the body against gravitation in both the cases are in ratio:

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1 : 2
0%
1 : 1
0%
2 : 1
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4 : 1

Explanation

$W=F. S$
As work done is independent of time. So, both the man does same work.
Hence, the work done on the body against gravitation are in ratio

$1:1$ .

The law of conservation of energy implies that the:

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Total mechanical energy is conserved
0%
Total kinetic energy is conserved
0%
Total potential energy is conserved
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Sum of all kinds of energies is conserved

In which one of the following cases is work done the maximum ?

0%
Mohan pushes against a wall for $30 \ minutes$
0%
Mohan pushes a bicycle which moves through a distance of $1.5 \ m$
0%
Mohan pushes a truck which does not move at all
0%
Mohan stands in the centre of his room

Explanation

Work done is defined as

$W = Fs\cos\theta$ , where

$F$ is the force applied,

$s$ is the displacement and

$\theta$ is the angle between force applied and displacement.

In cases A, C and D there is no displacement(

$s$ ) taking place.
So,

$W=Fs\cos\theta=0$ (as

$s=0$ )

In case B:

$s=1.5m$ so, Mohan does some work.

Hence, work done in case B is maximum.

So, option B is correct.

What is work done in holding a body of mass

$20\ kg$ at a height of

$2\ m$ above the ground?

$(g = 10\ m/s^2)$

0%
$40\ J$
0%
$400\ J$
0%
$10\ J$
0%
Zero

Explanation

A body of mass

$20\ kg$ is held at a height of

$2\ m$ above the ground means there is no displacement because of which there is no change in its potential energy. Hence work done is zero.

Which one of the following possesses kinetic energy?

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A moving car
0%
A compressed spring
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Water stored in the reservoir of a dam
0%
A car parked in the garage

Work done by static friction force when a person starts running is .......... .

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equal to the weight of the person
0%
zero
0%
infinite
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cannot be calculated

A vehicle travelling at

$30 \ m/s$ stops at a distance of

$50 \ m$ decelerating uniformly. A force of

$9000 \ N$ is exerted on it by the brakes. What is the work done by the brakes?

0%
$4.5 \times 10^4 \ J$
0%
$2.7 \times 10^5 \ J$
0%
$4.5 \times 10^5 \ J$
0%
$2.7 \times 10^4 \ J$

Explanation

The work done by the brakes is calculated using the relation ,

$W=F \times s$ ,

where

$F$ is the force applied and

$s$ is the displacement in the direction of force.

Hence,

$W=9000 \times 50=4.5\times 10^5 \ N$

How fast should a girl of 40 kg run so that her kinetic energy is 320J?

0%
64 m/s
0%
8 m/s
0%
16 m/s
0%
4 m/s

Explanation

Given, mass

$m=40kg , K.E=320J , v=?$

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

$320=\dfrac{1}{2}\times 40v^2$

$v^2=\dfrac{640}{40}=16$

$v=4m/s$
So, the girl of

$40$

$kg$ should run at

$4m/s$ so that her kinetic energy is

$320J.$

Energy conservation law says that:

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Energy can't be destroyed but can be produced.
0%
Neither energy can be produced nor can be destroyed.
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Energy can't be produced but can be destroyed.
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Energy can be produced and can be destoyed

A body at rest have:

0%
Energy
0%
Momentum
0%
Speed
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Velocity

Explanation

$\textbf{Step 1-Momentum of body}$

Here, body is at rest. So, it is not in motion means its speed and velocity both will be zero. Similarly, momentum is product of mass and velocity, so its value will be also zero.

$\textbf{Step 2-Energies of body}$

Kinetic energy of body which depends on velocity is also zero but it will have some potential energy which is given by the formula,

$U = m\ g\ h$ , where, m is mass, h is the height of body and g is the acceleration due to gravity.

So, its potential energy will not be zero.

And total energy is sum of both kinetic energy and potential energy. Which will be also non-zero.

So, a body at rest will have some energy.

Hence, option A is the correct answer.

The velocity of a bus, moving on a smooth road, is increased from 8 m/s to 32 m/s in 120s. During this process, the potential energy of the bus

0%
Does not change
0%
Becomes twice that of initial potential energy
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Becomes four times that of initial potential energy
0%
Becomes sixteen times that of initial potential energy

Explanation

As potential energy,

$P=mgh$
Since, there is no vertical displacement so,

$h=0$ .
Hence, potential energy change

$P=mgh=0$

The moving bus has only change in its Kinetic energy.

Two bodies P and Q of equal masses are kept at heights

$x$ and

$4x$ respectively. What will be the ratio of their potential energies?

0%
$1:8$
0%
$4:1$
0%
$1:4$
0%
$8:1$

Explanation

Potential energy

$P=mgh$
Given,

$h_1=x ; h_2=4x$

Since, the masses are same,
then

$\dfrac{P_1}{P_2}=\dfrac{h_1}{h_2} = \dfrac{x}{4x}=1:4$

An object of mass 500 g falls from a height of 2m. If

${g = 9.8 m/s^2}$ , what is its kinetic energy just before touching the ground?

0%
Zero
0%
19.6 J
0%
9.8 J
0%
9800 J

Explanation

We know,

Acceleration,

$a = \dfrac{v^2-u^2}{2s}$

where

$v$ and

$u$ are final and initial velocities respectively &

$s$ is the displacement.

Here,

$g = \dfrac{v^2-u^2}{2h}.$ Also,

$u=0$

$\implies$ Velocity when it touches ground,

$v=\sqrt{2gh}$

$v=\sqrt{2gh}=\sqrt{2\times9.8\times2}$

$K.E=\dfrac{1}{2}mv^2=\dfrac{1}{2}\times\dfrac{500}{1000}\times (\sqrt{2\times9.8\times2})^2$

$=\dfrac{1}{2}\times\dfrac{500}{1000}$

$\times2\times9.8\times2=9.8J$

A stone is projected vertically up to reach maximum height

$h$ . The ratio of its kinetic to potential energies at a height

$\cfrac{4h}{5}$ will be

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$5:4$
0%
$4:5$
0%
$1:4$
0%
$4:1$

What is the mass of a man if he does

$3600\ J$ of work in climbing a tree

$6\ m$ tall?

$({g = 10 m/s^2})$

0%
$70\ kg$
0%
$60\ kg$
0%
$85\ kg$
0%
$52\ kg$

Explanation

Work done,

$W=3600\ J$

Height of the tree,

$h=6\ m$

Acceleration due to gravity,

$g=10\ m/s^2$

Mass,

$m$

We know,

$W=Force\times distance$

$W=F\times h$

$\implies F=\dfrac Wh$

$\implies F=\dfrac {3600}{6}$

$F=600\ N$

Also,

$F=mg$

$\implies m=\dfrac {F}{g}$

$\implies m=\dfrac {600}{10}$

$m=6\ kg$

When a stone falls freely towards the earth, its total energy ?

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First decreases and then becomes zero
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Remains constant
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Increases
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Decreases

A car is being driven at a constant speed of

$5\ m/s$ by a force of

${3\times 10^8}\ N$ . It takes

$2$ minutes to reach its destination. What is the work done?

0%
${15\times 10^8\ J}$
0%
${18\times 10^{10}\ J}$
0%
${6\times 10^{10}\ J}$
0%
${10\times 10^8 \ J}$

Explanation

Given,

Speed,

$v=5\ m/s$

Time taken,

$t=2\ min$

$t = 2 \times 60=120\ s$

Force applied,

$F=3\times 10^8\ N$

Displacement,

$d$

We know,

$v=\dfrac dt$

$\implies d=v\times t$

$d=5 \times 120$

$d = 600\ m$

Work done,

$W=F \times d$

$W=3\times 10^8\times 600$

$W=18\times 10^{10}\ J$

The velocity of a ball goes on decreasing when it is thrown vertically upwards. When its velocity becomes zero, its potential energy becomes

0%
Minimum
0%
Maximum
0%
Zero
0%
9.8 J

A car is moving at

$100\ km/h$ . If the mass of the car is

$950\ kg$ , Its kinetic energy is:

0%
$367\ MJ$
0%
$0.367\ MJ$
0%
$3.67\ MJ$
0%
$3.67\ J$

Explanation

Mass of the car,

$m=950\ kg$

velocity of the car,

$v= 100\ km/h = { \left( 100\times \dfrac { 5 }{ 18 } \right) }$ m/s.

kinetic energy

$\displaystyle KE=\dfrac { 1 }{ 2 } \times m\times { v }^{ 2 }$

$\displaystyle =\frac { 1 }{ 2 } \times 950\times { \left( 100\times \frac { 5 }{ 18 } \right) }^{ 2 }J$

$\displaystyle =366512.35J=0.367\quad MJ$ .

Hence, the kinetic energy of the car is 0.367 MJ.

A girl weighing 50 kg makes a high jump of 1.2 m.What is her kinetic energy at the highest point?

${(g= 10 ms^{-2}}$ )

0%
6000 J
0%
600 J
0%
60 J
0%
Zero

Explanation

Given,

mass of girl

$M=50\ kg\\h=1.2\ m$

A girl is jumping vertically upward, when it will reach at maximum Hight its velocity will become zero

$v_f=0$

$K.E=\dfrac12 mv^2=\dfrac12m\times 0=0$

Option D

Which one of the following possesses both kinetic and potential energies?

0%
A man walking on the road
0%
A man climbing a hill
0%
A man lying on his bed
0%
A man running in the garden.

A body is under the action of two equal and opposite forces, each of 10 N. The body is displaced by 5 m.The work done is

0%
+50J
0%
-50J
0%
100J
0%
Zero

Explanation

Given

Applied forces

$F=10\ N$

Displacement

$=5$

As the situation given in the question,

Resultant force acting on the block

${F}{}_{net}=F+(-F)$

Hence

${F}{}_{net}=0$

$W={F}{}_{net} \times displacement\\ W=0\times 5=0$

$\therefore$ Work done is

$ZERO$

The spring of the winding knob of a watch has

0%
mechanical energy
0%
only kinetic energy
0%
only potential energy
0%
kinetic or potential energy

Explanation

We know that total energy is kinetic energy plus potential energy.

Now, kinetic energy is

$E=\frac { 1 }{ 2 } M{ V }^{ 2 }$

Which depends on velocity. In watch there is no displacement in the knob, hence velocity is zero. So there is no kinetic energy. Only potential energy is there.

The energy possessed by wind is

0%
kinetic energy
0%
potential energy
0%
thermal energy
0%
sound energy

CBSE Questions for Class 9 Physics Work And Energy Quiz 6 - MCQExams.com

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Practice Class 9 Physics Quiz Questions and Answers

CBSE Questions for Class 9 Physics Work And Energy Quiz 6 - MCQExams.com

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Practice Class 9 Physics Quiz Questions and Answers

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