MCQ Questions for Class 9 Physics Work And Energy Quiz 4

According to the law of conservation of energy, total energy is

0%
Increasing
0%
Decreasing
0%
Constant
0%
None of these

Which of the following physical quantities is different from others?

0%
Work
0%
Kinetic energy
0%
Force
0%
Potential energy

Explanation

Kinetic energy is the energy possessed by the body by virtue of its motion and potential energy is the energy possessed by the virtue of its position and shape. Energy is required to do work.

Hence work, kinetic energy, potential energy all can be measured using same unit, i.e joule.

So, force is the physical quantity here which is different from others as given by product of mass and acceleration. S.I unit of force is

$N$ (newton).

If work done by the net force is zero, work done by the individual forces needs to be zero.

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True
0%
False

A body is acted upon by a force that is proportional to the distance covered. If the distance covered is denoted by x, then work done by the force will be proportional to :

0%
$x$
0%
$x^2$
0%
$\displaystyle x^{\dfrac{3}{2}}$
0%
$x^4$

Explanation

Given :

$\text{The force is proportional to the displacement}$

$\therefore F \propto x \Rightarrow F = kx$

We know that

$\text{Work done}(W)=F.x$

$\therefore W= Fx = k.x.x=kx^2$

So,

$W\ \propto x^2$

One megawatt is .................... times that of one kilowatt.

0%
$1000$
0%
$19600$
0%
$100000$
0%
$0.001$

Explanation

One megawatt

$= 10^6$ Watt

One Kilowatt

$= 10^3$ Watt

$\implies \$ one megawatt

$= 1000$ kilowatt

If force and displacement of the particle (in direction of force) are doubled, Work should be :

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Doubled
0%
Quadrupled
0%
Halved
0%
Reduced by $\displaystyle \frac{1}{4} times$

Explanation

Work done is defined as

$W=Fs$

where

$F$ is the force applied and

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

Hence initially work done

$W_1 = Fs$

Now, When

$F_2=2F$ and

$s_2=2s$

Then, work done

$W_2=F_2s_2$

$\Rightarrow W_2=(2F)(2s)$

$\Rightarrow W_2 = 4W_1$

Hence, work done is quadrupled.

When a force retards the motion of a body, the work done is :

0%
Zero
0%
Negative
0%
Positive
0%
Positive or negative depending upon the magnitude of force and displacement

The work done in holding

$15\ kg$ suitcase while waiting for a bus for

$45$ minutes is :

0%
$675\ J$
0%
$40500\ J$
0%
$4500\ J$
0%
$Zero$

Explanation

Work done = force

$\times$ displacement in force direction

Work done in holding a suitcase while waiting for a bus i.e. stationary position.

So, displacement will be zero.

Work done = force

$\times$ zero

Work done = zero

$1 \ N$ of the force displaces the body through

$1 \ m$ in the direction of force, then the work done is said to be ______.

0%
$1 \ J$
0%
$1\ N-m$
0%
$1 \ N-cm$
0%
none of the above

Explanation

Work done by any force is given by product of force and displacement of the particle and cosine of angle

$\theta$ between them.

$W=Fs \cos\theta$

where

$F$ is force applied and

$s$ is the displacement of the particle,

SI Unit of work done is

$N-m$ and also called

$Joule (J)$ .

So work done in above case is

$W=Fs$ , here

$\theta=0$

Given

$F = 1\ N, \ \ \ \ s = 1 \ m$

$W=1 \ J \ \ \ or \ \ \ 1\ N-m$ .

So possible answers are A and B.

Choose the correct option.

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$kW=$ unit of power and $kWh =$ unit of energy.
0%
$kW=$ unit of energy and $kWh =$ unit of power.
0%
$kW$ and $kWh$ are both of unit of energy.
0%
$kW$ and $kWh$ are both of unit of power.

Explanation

Electrical Power is measured in watts (

$W$ ), kilo-watts (

$kW$ ), mega-watts (

$MW$ ), and giga-watts (

$GW$ ).

Electrical Energy is measured in kilowatt-hours (

$kWh$ ), megawatt-hours, and sometimes (less commonly) in watt-hours or watt-seconds.

How much work is done by a force 50 N moving an object through a distance 10 m in the direction of force ?

0%
$5 \ J$
0%
$500\ J$
0%
$0.5\ J$
0%
$0\ J$

Explanation

$F=50N$

$s=10m$

Work done,

$W=F\times s=50\times 10=500J$

A boy carrying a box on his head is walking on a level road from one place to another on a straight road is doing no work against gravity.

0%
True
0%
False

Explanation

The force of gravity is perpendicular to the direction of displacement of the boy.

Work = force

$\times$ displacement in the direction of force

In this case, displacement is zero along with the force because the boy is moving horizontally and the force(

$mg$ ) acting downward.

Hence, zero work is done.

What will be the potential energy of a body of mass 5 kg kept at a height of 10 m ?

0%
50 J
0%
0.5 J
0%
500 J
0%
25 J

A fish swimming in water possess mechanical energy.

0%
True
0%
False

The work done by a force on a body will be positive if the body -

0%
Moves perpendicular to the direction of applied force
0%
Does not move
0%
Moves along the direction of applied force
0%
Moves opposite to the direction of applied force

Explanation

Work done is positive when the force is in the direction of displacement.

$\text{work} = \text{Force} \times \text{displacement in the direction of force}$

An electric toaster draws

$8\ A$ current in a

$220\ V$ circuit. It is used for

$2\ hr$ . What is the cost of operating the toaster if the cost of electrical energy is

$Rs.\ 4.5 / kWh$ ?

0%
$Rs.\ 9.50$
0%
$Rs.\ 25.50$
0%
$Rs.\ 14.84$
0%
$Rs.\ 15.84$

Explanation

Given,

$i=8\ A\\E=220\ v\\t=2\ hr$

Energy dissipated is given by:

$E = E\ i\ t$

$=220 \times 8 \times 2\ Wh$

$=3.52\ kWh$

The cost per kWh is

$Rs.\ 4.50$

Hence, the cost of running the kettle for two hours is:

$3.52 \times 4.50 = Rs.\ 15.84$

In our household applications, commercial unit of electricity is used. One unit is equal to:

0%
$1\ kW$
0%
$1\ kWh$
0%
$1\ kW/h$
0%
$1\ Wh$

A machine raises a load of

$750N$ through a height of

$16m$ in

$5s$ . Calculate work done by machine:

0%
$12000 kJ$
0%
$12 kJ$
0%
$1200 J$
0%
$120 kJ$

Explanation

We know that

$Work = F\times s$
Here,

$F = 750\ N$ and

$s=16\ m$ .

$W = 750\times16 = 12000\ J = 12\ kJ$

A pump is used to lift

$500\ kg$ of water from a depth of

$80\ m$ in

$10\ s$ .

(Take

$g=10\ ms^{-2}$ ). Calculate the work done by the pump.

0%
$16 \times 10^5J$
0%
$4\times 10^5J$
0%
$4\times 10^8J$
0%
$2\times 10^5J$

Explanation

Given,

Mass of water lifted,

$m=500\ kg$

Displacement,

$d=80\ m$

Time taken,

$t=10\ s$

Force,

$F = m\times g$

$F = 500\times 10$

$F= 5000\ N$

Work done,

$W= F\times d$

$W = 5000\times 80$

$W = 4\times 10^{5}\ J$ .

A body when acted upon by a force of

$10\ kgf$ , gets displaced by

$0.5\ m$ . Calculate the work done by the force, when the displacement is in the direction of force.

0%
$5 J$
0%
$500 J$
0%
$0.5 J$
0%
$50J$

Explanation

Given -

$F = 10\ kgf$ and

$s = 0.5\ m$ in the direction of force.

$1 Kgf = 10 N$

$\implies F = 10kgf = 10 \times 10N = 100N$

$W = F \times s$

$W = 100 \times 0.5$

$W = 50 J$

A boy carrying a box on his head is walking on a level road from one place to another. The work done by him against the gravitational force is zero. This statement is :

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correct
0%
incorrect
0%
partly correct
0%
insufficient data

A man spends

$6.4 \ kJ$ energy in displacing a body by

$64 \ m$ in the direction in which he applies force, in

$2.5 \ s$ .

Calculate the force applied.

0%
$1N$
0%
$10N$
0%
$0.1N$
0%
$100N$

Explanation

We know that

$Work = Force \times displacement$ .

Here, given

$Energy = 6.4\ kJ = 6400\ J$

$\implies Work =64000J$ and

$displacement = 64\ m$ .

$Force = \dfrac{Work}{displacement} = 6400/64 = 100 N$ .

Name the type of energy (kinetic energy

$K$ or potential energy

$U$ ) possessed in the following case.

The bob of a simple pendulum at its extreme position.

0%
$K$
0%
$U$
0%
$K$ and $U$
0%
No energy

Explanation

Here simple pendulum is at a certain height and at extreme position it will not have any velocity. Hence , kinetic energy will be zero. Whereas

$U = m\times g\times h$ .

As it is at certain height it has some value for

$h$ . Hence, it will have certain potential energy.

A man raises a box of mass

$50 \ kg$ to a height of

$2 \ m$ in

$2 \ minutes$ , while another man raises the same box to the same height in

$5 \ minutes$ . What is the ratio of work done by them ?

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

Explanation

$Work = Fs\cos\theta$

where,

$F$ is the force applied,

$s$ is the displacement, and

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

Hence, work done is independent of time taken.

In the given cases,

$\theta = 0^{\circ}$ as the force applied are in the same direction. Also,

$F=mg$

$W=Fs=mgs$

In both the cases, mass and displacement are the same.

$W =50\times 10\times 2 = 1000 J$

Hence work done is in the ratio of

$1000 : 1000 = 1:1$ .

Before a rubber ball bounces off from the floor, the ball is in contact with the floor for a fraction of second. Which of the following statements are correct?

0%
Conservation of energy is not valid during this period
0%
Conservation of energy is valid during this period
0%
Only the kinetic energy is conserved
0%
Only the potential energy is conserved

Explanation

$\text{The total energy of the ball} =\text{Kinetic Energy}+\text{Potential Energy}$

The kinetic energy or the potential energy changes as the ball falls down and hits the floor. But the total energy is always conserved.

An electric heater of power

$3 \ kW$ is used for

$10 \ h$ . How much energy does it consume? Express your answer in joule.

0%
$1.08\times 10^5$
0%
$1.08\times 10^8$
0%
$1.08\times 10^7$
0%
$1.08\times 10^3$

Explanation

We know that

$Power = work/time$

$Work \ or\ energy = Power\times time$

$Work = 3 kW \times 10 h$

$Energy = 30 KWh$ .

$Energy = 30\times 10^{3}\times 60\times 60\times =1.08\times 10^{8}\ J$ .

A body is moved in a direction opposite to the direction of force acting on it. Work is done is:

0%
against the force
0%
zero
0%
along the force
0%
none of these

Explanation

Here force and displacement is in opposite direction. Hence, negative work is done i.e, against the direction of force.

Work done is given by formula -

$W = (-F )\times s$

Write an expression for the work done when a force is acting on an object in the direction of its displacement.

0%
$Force \times Displacement$
0%
$Force \times velocity$
0%
$Force \times acceleration$
0%
$Force \times Distance$

Explanation

Correct option: A

Explanation for correct option:

$\textbf{Part1: Definition of work done}$

Work is said to be done when the force applied to an object shows the object’s displacement.

$\textbf{Part2: Expression of work done}$

When a force F displaces a body through a distance S in the direction of applied force, then the work done W, on the body is given by the expression:

$Work = Force \times Displacement$

$\Rightarrow W = F \times S$

Hence, the correct option is A.

Name the type of energy (kinetic energy

$K$ or potential energy

$U$ ) possessed in the following case.

A piece of stone placed on the roof.

0%
$U$
0%
$K$
0%
$U$ and $K$
0%
No energy

Explanation

When a stone is placed at the roof it is at a certain height that is given by

$U = m\times g\times h$

As we have a certain value for

$h$ there would be some value for potential energy.

As the stone is at rest at the roof it will not have any kinetic energy as its velocity is zero,

$K = 1/2 (m\times v^{2})=0$ .

Hence, only potential energy will be there.

State whether the given statement is True or False :

The energy of an object that is due to the object's motion is called kinetic energy.

0%
True
0%
False

Explanation

The kinetic energy of an object is the energy it possesses because of its motion. The kinetic energy of a point mass m is given by
K.E

$=\frac1 2m\times v^2$

CBSE Questions for Class 9 Physics Work And Energy Quiz 4 - MCQExams.com

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Practice Class 9 Physics Quiz Questions and Answers

CBSE Questions for Class 9 Physics Work And Energy Quiz 4 - MCQExams.com

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Practice Class 9 Physics Quiz Questions and Answers

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