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CBSE Questions for Class 9 Physics Work And Energy Quiz 5 - MCQExams.com
CBSE
Class 9 Physics
Work And Energy
Quiz 5
The gravitational potential energy possessed by a body is by virtue of its _________.
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position
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velocity
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acceleration
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temperature
Explanation
The energy possessed by a body by virtue of its position is called gravitational potential energy
According to the law of conservation of energy:
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Energy exists in only one form.
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Energy can be created but not be destroyed, and it can be transformed from one form to another.
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Energy exists in many forms but it cannot be transformed.
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Energy can neither be produced nor be destroyed and it can be transformed from one form to an-other form.
Explanation
According to the law of conservation of energy, energy can neither be produced nor be destroyed and it can be transformed from one form to another.
An energy of $$4 kJ$$ causes a displacement of $$64 m$$ in $$2.5 s$$. The power delivered is
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$$16 W$$
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$$160 W$$
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$$1600 W$$
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$$16000 W$$
Explanation
Given that:
Energy, $$E=4\ kJ=4000\ J$$
Time taken, $$t=2.5\ sec$$
Power delivered , $$P=\dfrac Et=\dfrac{4000 \ J}{2.5 \ sec}= 1600\ W$$
Option C is correct.
A pair of bullocks exerts a force of 140 N on a plough. The field being ploughed is 15 m long. How much work is done in ploughing the length of the field ?
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$$1200 \: J$$
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$$4800 \: J$$
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$$2100 \: J$$
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$$2400 \: J$$
Explanation
HINT:
Use work done formula.
$$\textbf{Step1:Work done by Force}$$
If angle between force and displacement is $$\theta$$ then work done by force is
$$W={\vec F}.{\vec S}$$
$$W=FS {\cos \theta}$$
$$\textbf{Step2:Work done in ploughing the field}$$
Given force $$F = 140\;N$$
Displacement $$S = 15\;m$$
According to question angle between force and displacement is zero.
Work done $$W = F S cos0=FS$$
$$= 140 \times15$$
$$= 2100\;Nm = 2100\;J$$
Option C is correct.
The energy consumed by $$100 \ W$$ electric bulb in $$5 \ hours$$ is:
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$$0.5 \ kWh $$
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$$1.5 \ kWh $$
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$$5 \ kWh $$
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$$2.5 \ kWh $$
Explanation
Given, power of the electric bulb,
$$P =100 \:W=\dfrac{100}{1000} \:kW=0.1 \:kW$$ ;
time for which bulb is used, $$t =5 \:h$$
As $$\displaystyle P =\frac{W}{t}$$ or $$W =Pt$$
or $$W =0.1 \:kW \times 5 \:h =0.5 \:kWh $$
A man is waiting for a bus. What is the work done when he is carrying a box and waits for 5 minutes for the bus?
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$$200 \ J$$
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$$100 \ J$$
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$$6000 \ J$$
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$$0 \ J$$
Explanation
$$ W = Fs\cos\theta$$
where $$W$$ - work done, $$F$$ - force, $$s$$ - displacement, $$\theta$$ - angle between force and displacement
As there is no displacement $$s = 0$$
.
Hence work done is zero. $$W=0$$
By stretching the rubber strings of a catapult we store .......... energy in it.
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$$potential$$
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$$electrical$$
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$$heat$$
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$$kinetic$$
Explanation
Answer: Potential Energy
The energy exerted or work done by our muscles on the rubber band is consumed in changing its shape. It gets stored in the stretched rubber band as its potential energy. It is this stored energy that is used by the rubber band to move to its original state, shape, and size. When the rubber band is released, this stored potential energy gets converted into kinetic energy.
If a pebble is placed in contact with the stretched rubber band, this kinetic energy is transferred to the pebble. This kinetic energy of the pebble is enough to do some destructive work, like breaking a glass window, injuring someone, etc.
A force of 7 N acts on an object. The displacement is 8 m, in the direction of the force. Consider force acting on the object through the displacement. What is the work done in this case ?
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$$96 \: J$$
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$$56 \: J$$
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$$76 \: J$$
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$$156 \: J$$
Explanation
$$Given, \: force =7 \: N \;; \: displacement = 8 \: m $$
$$Work \: done = Force \times Displacement$$
$$= 7 \times 8 = 56 \: J$$
An engine pulls a train 1 km over a level track. Calculate the work done by the train against friction if frictional force is $$5 \times 10^5 N$$.
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$$5 \times10^8J$$
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$$5 \times10^4J$$
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$$8 \times10^8J$$
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$$6 \times10^8J$$
Explanation
Given, frictional force, $$F = 5 \times 10^5 N$$ ;
Displacement of the train, $$s =1 \:km =1000 \:m$$
Work done by the train against
frictional force,
$$W =F \times s = (5 \times 10^5) \times(1000) =5 \times10^8J$$ .
The work done is dependent on following quantities:
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Force
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Mass
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Distance
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All of the above
Explanation
Work done is given by : $$Work (W) = Force\ applied (F) \times Distance \ traveled \ in \ direction \ of \ force (d) $$
So, $$ W = F \times d $$
where $$ Force(F) = Mass (m) \times Acceleration (a)$$
So, work depends on force, mass, and distance
So, option D is the correct answer
Work done =
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Force $$\times $$ velocity
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Force $$\times $$ displacement
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Force $$\times $$ time
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Power $$\times $$ velocity
Explanation
Hint:
Whenever a force $$F$$ acts on a body and that body moves by certain distance because of that force, Work is said to be done by that force on that body.
Correct Option is B.
Explanation for the correct answer:
By definition of work done by any force, If any force $$f$$ acts on any body, and because of that force let body is displaced by displacement $$x$$ in the direction of force, then work done is the product of force with the displacement in the direction of force.
That is,
$$W = f . x$$
Option B is correct.
Work done is said to be positive if the applied force and the displacement are in ............ direction.
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Same
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Any
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Opposite
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Perpendicular
Explanation
Work done is positive when the force is in the direction of displacement.
When an arrow is released from a bow, potential energy changes into kinetic energy.
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True
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False
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Ambiguous
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Data insufficient
Explanation
When an arrow is drawn back by a bow, the work done by us in stretching the bowstring gets stored at potential energy in the bow. This potential energy of bow is transformed into kinetic energy when the bowstring is released and this gives kinetic energy to the arrow.
According to law of conservation of energy the total energy of the universe is:
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Increasing
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Decreasing
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Remains constant
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Above law does not say anything about the universe
Explanation
Law of conservation of energy states that ''Energy can neither be created nor destroyed'. Hence total energy remains constant for the isolated system. Universe can consider as an isolated system so its total energy will remains same.
An object in a given position can have a certain potential energy with respect to one level and a different value of potential energy with respect to another level.
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True
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False
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Ambiguous
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Data insufficient
Explanation
Potential energy of an object always defined with respect to reference point. If location of reference point changes, there is a possibility that potential at that point would change.
In general, we write the potential energy of an object at a height $$h$$ from earth surface $$U=mgh$$. Here we take earth surface as a zero potential level or reference point.
Hence, Given statement is true. Option A
Four men lift a 250 kg box to a height of 1 m and hold it without raising or lowering it. How much work is done by the men in lifting the box? $$(g=10 \:m \:s^{-2})$$
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2000 J
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4000 J
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2500 J
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1500 J
Explanation
Given, mass m = $$250\ kg$$ and height = $$1\ m $$
We know,
Work done$$\ =F.S$$
$$\ =(m \times g)\times1$$
$$\ =250\times10\times1$$
$$\ =2500 J$$
A car is accelerated on a levelled road and attains a velocity 4 times of its initial velocity. In this process, the potential energy of the car
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does not change
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becomes twice of initial
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becomes 4 times of initial
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becomes 16 times of initial
Explanation
Answer is A.
The potential energy is the energy that an object has due to its position in a force field or that a system has due to the configuration of its parts.
The potential energy of the car remains the same
and will not change as the road is leveled and the height of the body remains the same, although its speed increases.
When a body falls freely towards the earth, then its total energy
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increases
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decreases
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remains constant
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first increases and then decreases
Explanation
Correct Option is C.
Explanation for the correct answer:
$$\bullet$$ A freely falling body is free from the non conservative and external forces, thus we can apply Conservation of Energy in such a case.
$$\bullet$$ By Conservation of Energy, the Total Energy of the body remains conserved, that is constant.
$$\bullet$$ As the body falls its Potential Energy starts converting into the Kinetic Energy, and the Total Energy remains same.
Option C is correct.
Potential energy of a body depends on its:
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motion
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colour
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mass
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none of these
Explanation
We know that potential energy is the energy possesd by the virtue of its position.
So, $$F = mgh $$
Where, $$ m = $$ mass
So, From above equation we can deduce that potential energy depends on the mass of the substance.
Calculate the work done when a $$2\ N$$ 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
Given,
Force applied, $$F= 2\ N$$
Distance travelled, $$s = 10\ m$$
We know,
$$Work\ done = Force\ applied \times Distance \ moved$$
$$W = F \times s$$
$$W = 2 \times 10$$
$$W = 20\ J$$
Flowing water has the capacity to do work
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True
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False
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Both
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None
Explanation
Flowing water possess kinetic energy which is used to do work.
A boy is pushing hard on a wall. Is he doing work?
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No
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Can't say
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May have done some work
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Yes
Explanation
$$\text{Work}=\text{Force}\times \text{Displacement}$$
Here, the wall is not moving although the boy is pushing hard. $$\therefore \text{Displacement}=0$$
$$\therefore \text{Work}=0$$
Energy possessed by a body by virtue of its motion is :
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Potential energy
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Kinetic energy
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Chemical energy
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Electrical energy
Explanation
Kinetic energy is defined as the energy possessed by a body by virtue of its motion. and it is equal to
$$ K.E. = \cfrac{1}{2}mv^{2} $$ Where $$m$$ and $$v$$ are mass and Velocity of moving body.
A student sitting at the top of a tree has ............ than the student who is sitting on the ground.
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less potential energy
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more potential energy
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more kinetic energy
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more gravitational energy
Explanation
Potential energy = $$mgh$$
$$m\rightarrow mass$$
$$g\rightarrow acceleration\ due\ to\ gravity$$
$$h\rightarrow height\ from\ ground$$
P.E. is directly proportional to the height from the ground. Hence a student sitting at the top of a tree has more potential energy than the student who is sitting on the ground.
If an object remains stationary even when force is applied then:
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Work is said to be done
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Work is not done
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Work may have been done
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Work cannot act on that body
Explanation
$$\text{Work}=\text{Force}\times \text{Displacement}$$
Work is said to be done only when the body is displaced from its original position by an applied force on it. If the body does not displace then no work is being done even if the force is acting on the body.
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
Explanation
The kinetic energy of a body is the energy by virtue of its motion.
$$ K.E = \dfrac{1}{2}mv^2 $$
where $$m$$ is mass and $$v$$ is velocity.
Hence, Kinetic energy is directly related to the speed of a moving body and its mass.
A heavy object has ---- 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
$$P.E= mgh$$
The amount of potential energy an object possesses depends on its height and mass. The heavier the object and the higher from the ground, the more potential energy it holds.
Energy possessed by a body by virtue
of its position at a height is :
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Kinetic energy
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Chemical energy
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Potential energy
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Magnetic energy
Explanation
The potential energy of a body is defined as energy possessed by a body by virtue of its position at a height.
$$ P.E = mgh$$
$$m$$: mass of the object
$$g$$ : gravitational acceleration
$$h$$: height gained by object
Two weights of 5 kg and 10 kg are placed on a horizontal table of height 1.5 m. Which will have more potential energy?
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5 kg
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10 kg
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Both will have equal energy
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None of the above
Explanation
We know that , P.E $$ = mgh $$
So, It is directly proportional to height and mass.
Since both the weights are at the same height, so the weight with a larger mass will have more potential energy.
Since $$10$$kg object has a larger mass than a $$5$$ kg,
so, the potential energy of a $$10$$kg mass will be greater.
Which one of the following possesses potential energy?
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Moving vehicle on the road
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A running athlete
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Stone on the road
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A stretched rubber band
Explanation
Moving vehicle on the road possesses kinetic energy.
A running athlete possesses
kinetic energy.
Stone on the road possesses
kinetic energy.
A stretched rubber band possesses potential energy.
Hence, option D is correct.
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