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CBSE Questions for Class 9 Physics Work And Energy Quiz 8 - MCQExams.com
CBSE
Class 9 Physics
Work And Energy
Quiz 8
An electric heater has a rating of 2 kW, 220 V. The cost of running the heater for 10 hours at the rate of Rs 350 per unit is Rs ____
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216
0%
165
0%
209
0%
105
Explanation
Power is energy consumed per unit time.
Here, energy consumed$$=P=2kW=2000W$$ and time$$=t=10hr=36000s$$
$$P=\dfrac{E}{t}$$
$$\implies E=Pt=2kW\times 10h=20kWh=20units$$
Since $$1unit=1kWh$$
Cost$$=20\times 350=Rs 7000$$
What is the work done by gravity on a load of $$50 \ kg$$ carried by porter while walking along the platform?
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$$0 J$$
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$$10 J$$
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$$50 J$$
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$$500 J$$
Explanation
Force of gravity and displacement of load carried by the porter are perpendicular to each other.
Hence, work done by gravity on the load is zero.
The energy directly related to the speed of a moving body and its mass is:
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kinetic
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potential
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solar
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electric
A heavy object has ....... gravitational potential energy than a lighter one.
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less
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more
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same
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none of these
Explanation
Gravitational potential energy is given by
$$PE=mgh$$
where $$m$$ is mass so heavy object means more mass and more mass means more potential energy.
The electricity tariff in a town is $$Rs.3.00$$ per unit. Calculate the cost of running an $$80 W$$ fan for $$10 h$$ a day for the month of June.
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$$Rs. 12.00.$$
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$$Rs. 52.00.$$
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$$Rs. 72.00.$$
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$$Rs. 92.00.$$
Explanation
Total time for which the fan is used $$= (10 hours) \times (30 days) = 300$$ hours.
Energy consumed $$= (80 W) \times (300$$ hours$$)$$
$$= 24,000 Wh = 24 kWh.$$
But $$1 kWh =1$$ unit.
Therefore, $$24 kWh = 24$$ units
The cost of this power $$= 24$$ units $$\times Rs. 3= Rs. 72.00.$$
Which one of the following types of energy is possessed by a body when placed at a certain height?
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Kinetic energy
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Potential energy
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Heat energy
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Sound energy
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None of these
Explanation
When a body is placed at a certain height, the body possesses potential energy.
$$P.E. = mgH$$
$$m$$; the mass of the object
$$g$$; acceleration due to gravity
$$H$$; height gained by object
Calculate the work done when a 2N force moves a body through a distance of 10 m.
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10 J
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2 J
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5 J
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20 J
Explanation
Work done
= Force applied x Distance moved
$$W=F \times s$$
$$ W = 2 \times 10 = 20\ J $$
------ is done when you push a box
.
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Displacement
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Motion
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Work
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Speed
Explanation
When we push a box, a force is applied. Since the box is moving, some work is done on the box. (As $$Work=(force)\times (displacement)$$
Potential energy increases :
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As the height increases
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As the mass decreases
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As the velocity increases
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None of the above
Explanation
Potential energy of an object of mass $$m$$ at height $$h$$, $$ P.E = mgh$$
$$\implies P.E \propto h$$
Therefore, potential energy increases as the height increases.
Find the potential energy if a body is placed at a certain height of 5 m from the earth.
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196 J
0%
200 J
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150 J
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300 J
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None of these
The water stored in a reservoir
possesses :
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Kinetic energy
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Muscular energy
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Potential energy
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Magnetic energy
Explanation
Potential energy is the energy possessed due to the relative position of one body with respect to other.
Kinetic energy is the energy possessed due to the motion of the body.
Water stored in the reservoir is at rest, so no kinetic energy
but it is at some height with respect to some level below the water surface, so it contains potential energy.
Two masses $$10 \ gm$$ and $$40 \ gm$$ are moving with kinetic energies in the ratio $$9:25$$. The ratio of their linear momentum is:
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$$5:6$$
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$$3:10$$
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$$6:5$$
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$$10:3$$
When an aeroplane takes off from
the ground :
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Kinetic energy increases and Potential energy decreases
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Potential energy increases and Kinetic energy remains constant
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Both Kinetic energy and Potential energy remain constant
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Both Kinetic energy and Potential energy increase
Explanation
Kinetic energy is due to the motion of the object and potential energy is due to relative elevation.
So as the plane takes off height increases and also its speed increase, so both kinetic and potential energy increases.
$$\text{Kinetic energy} = \dfrac{1}{2}mv^2$$
$$\text{Potential energy} = mgH$$
Which of the following is an example
of an object with Kinetic energy?
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Boy running on field
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Bent bow
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Stone at a height
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Water stored in a reservoir
Explanation
kinetic energy is energy possessed by body due to virtue of its motion.
only boy in option A is in motion so only he has some kinetic energy.
rest option have things at rest so no kinetic energy.
so option A is the answer.
While running you possess certain kind of energy due to motion .What kind of energy do you possess?
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Potential energy
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Kinetic energy
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Electrical energy
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Chemical energy
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None of these
Explanation
The energy possessed by the virtue of motion of any object is called kinetic energy.Hence while running the energy possessed by the person is kinetic energy.
Kinetic energy of a body depends on its:
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Position
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Velocity
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Shape
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Colour
Explanation
$$K.E.=\dfrac{1}{2} mv^2$$
So the kinetic energy of a body depends upon its mass and velocity.
A force, applied on a body, is said to have done some work
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If the body suffers no displacement
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If the body suffers a displacement
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If the shape of the body changes
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If the size of the body changes
Explanation
A force, applied on a body, is said to have done some work if the body suffers a displacement. This is according to the definition of work.
$$\text{work = Force} \times \text{displacement}$$
.............. is said to be done only when the force applied on a body makes the body to move.
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Work
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Momentum
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Retardation
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None of these
Explanation
Work is said to be done when the force applied to a body makes the body move. By definition 'Work = Force x Displacement.
A body is moved in a direction opposite to the direction of force acting on it. So:
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work is done by the force
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work is done against the force
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no work is done
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an infinite amount of work is done
Explanation
When displacement is in a direction opposite to the direction of force acting, work is said to be done against the force applied.
Option B
The CGS unit of energy is :
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Dyne
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Erg
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Centimetre
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Pascal
Explanation
CGS unit of energy is $$Dyne-cm$$ which is also known as $$erg$$.
Which of the following does not have
potential energy ?
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An inflated balloon
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Water in a flowing river
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A fruit on the tree
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A spinning top
Explanation
Potential energy is the energy that is stored in an object due to its position above the ground surface and when the object is in motion then it has kinetic energy.
Water in a flowing river has kinetic energy.
From the following statements find the one that is NOT correct :
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A flying bird has both potential and kinetic energy
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A ball rolling on the ground has kinetic energy but no mechanical energy
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A stretched rubber band has potential energy.
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Chemical energy can be converted into electrical energy
Explanation
The energy of an object by virtue of its motion is known as potential energy.
The energy possessed by a body due to its change in position or shape is called potential energy. For example, A stretched rubber band.
The sum of kinetic energy and potential energy
of an object is its total mechanical energy.
A flying bird has both potential and kinetic energy.
A ball rolling on the ground has kinetic energy Therefore, it also has mechanical energy.
Chemical energy can be converted into electrical energy. For example, a battery.
In which of the following cases, is a work being done?
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A boy pushing a wall
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A coolie walking with a load of 10 kg on his head
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A girl is climbing up the staircase
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A student is holding a book in hand
Explanation
A) For a boy pushing a wall, there is no displacement of the wall. So, the work done is zero.
B) For a coolie carrying a load on his head, the force applied by the coolie is against the gravity, i.e., the force is vertically upward. And the displacement of the load is horizontally forward. So, the force and the displacement are perpendiculars. This means the work done is zero.
D) Similarly, for a student holding a book in his hands, force is applied against the gravity and the displacement is zero. Hence, the work done is zero.
C) For a girl climbing up the stairs, force is applied against the gravity and the displacement is also upward, i.e., in the direction of the force. So, only here work is done.
A boy of mass $$40\ kg$$ runs up a flight of $$50$$ steps, each $$10\ cm$$ high in $$14\ s$$. So, work done by the boy is:
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$$1960\ J$$
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$$19.6\ J$$
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$$980\ J$$
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$$9.8\ J$$
Explanation
Mass of the boy, $$m = 40\ kg$$
Number of steps = $$50$$
Height of each step = $$10\ cm$$
Force on the boy due to gravity, $$F=mg=40\times{9.8}N=392\ N$$
While climbing up the steps, the boy does work against gravity.
Displacement in the vertical direction, $$s=(50\times{10})\ cm=500\ cm=5\ m$$
Displacement is in the direction of force applied by the boy against gravity.
So, work done, $$W=F\times{s}=392\times{5}\ J=1960\ J$$
A moving cricket ball possesses
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Kinetic energy
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Potential energy
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Chemical energy
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Sound energy
Explanation
A moving cricket ball possesses kinetic energy.
Formula of kinetic energy$$(KE)$$-
$$KE = \dfrac{ 1 }{ 2 }mv^2$$
$$m$$; mass of the ball
$$v$$; speed of the ball
Work in terms of power and time
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$$\text{power} \times \text{time}$$
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$$\dfrac{\text{power}}{\text{time}}$$
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$$\text{power}+\text{time}$$
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None of these
Explanation
The power is-
$$Power = \dfrac{Work}{time}$$
$$\Rightarrow work = power \times time$$
Work done by a fielder in catching a ball is
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Zero
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Positive
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Negative
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None of these
Explanation
To catch a ball, the fielder has to stop the ball. This means, force is applied against the motion of the ball. So, the fielder applied the force on the ball and
the ball moves in the direction opposite to the direction of force till
the ball comes to rest, . Thus work is negative.
The amount of work done (or, energy spent) by a source of power $$1kW$$ in $$1h$$ time is:
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$$1J$$
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$$1Wh$$
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$$1kWh$$
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$$1calorie$$
Explanation
$$Energy$$ $$spent$$ = $$Power \times time$$
$$E=1kWh \times 1h$$ =
$$1kWh$$
$$1kWh$$ is the amount of work done (or, energy spent) by a source of $$1kW$$power in $$1h$$ time.
The S.I. unit of energy is
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erg
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calorie
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Joule
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None of these
Explanation
Energy is capacity of doing work. The unit of energy is same as that of work. So, S.I. unit of energy is $$joule(J)$$.
A fruit hanging from the top branch of a tree possesses
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gravitational potential energy
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elastic potential energy
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kinetic energy
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sound energy
Explanation
A fruit, hanging from the top branch of a tree, is at rest at a certain height from the earth"s surface.
So, it possesses gravitational potential energy.
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