CBSE Questions for Class 9 Physics Work And Energy Quiz 14 - MCQExams.com

Some children were trying to find out which of three bulbs was brightest. Which one of these gives the best start toward finding the answer?
  • "One bulb looks the brightest to me, so I already know the answer."
  • "It would help if we had a way to measure the brightness of a light bulb."
  • "All the bulbs look bright to me, so there cannot be an answer."
  • "We can take a vote and each person will vote for the bulb he or she thinks is the brightest ."
A man carries a heavy box on his head on a horizontal plane from one place to another. In this case, he does
  • Maximum work
  • No work
  • Negative work
  • Minimum work
When a body does some work its energy decreases. 
  • True
  • False
A car weighing 600 kg traveling with $$72\, km/h$$ stops at a distance of $$60\ m$$ decelerating uniformly. What is the work done by brakes in joules?
  • $$1.2 \times 10^5\ J$$
  • $$2.4 \times 10^5\ J$$
  • $$3.2 \times 10^5\ J$$
  • $$1.4 \times 10^5\ J$$
1 kWh is equal to
  • $$3.6 \times 10^6 MJ$$
  • $$3.6 \times 10^5 MJ$$
  • $$3.6 \times 10^2 MJ$$
  • $$3.6 MJ$$
Energy cannot be measured in.
  • $$Js^{-1}$$
  • $$Ws$$
  • $$kWh$$
  • $$erg$$
In which of the following, work is being done?
  • Man sitting on a bench
  • Person Standing with a basket of fruit on the head.
  • Climbing a tree to pluck.
  • Pushing a wheelbarrow of bricks.
Sunil rolls a marble ball down a frictionless inclined plane as shown above. What kind of energies are possessed by the rolling marble ball?

85200_9f941723bcc140f88767f1935dfbfba4.png
  • (i) and (ii) only
  • (ii) and (iii) only
  • (iii) and (i) only
  • (i), (ii) and (iii)
Work done in time $$t$$ on a body of mass $$m$$ which is accelerated from rest to a speed $$v$$ in time as a function of time $$t$$ is given by
  • $$\cfrac { 1 }{ 2 } m\cfrac { v }{ { t }_{ 1 } } { t }^{ 2 }\quad $$
  • $$m\cfrac { v }{ { t }_{ 1 } } { t }^{ 2 }$$
  • $$\cfrac { 1 }{ 2 } m{ \left( \cfrac { v }{ { t }_{ 1 } } \right) }^{ 2 }{ t }^{ 2 }$$
  • $$\cfrac { 1 }{ 2 } m\cfrac { v }{ { t }_{ 1 }^{ 2 } } { t }^{ 2 }$$
A weight lifter lifts a weight off the ground and holds it up then:
  • Work is done in lifting as well as holding the weight
  • No work is done in both lifting and holding the weight
  • Work is done in lifting the weight but no work is required to hold it up
  • No work is done in lifting the weight but work is required to be done in holding it up
 A particle is taken from A to point B under the influence of a force field. Now it is taken from B to A and it is observed that the work done in taking the particle from A to B is not equal to the work done in taking it from B to A. If $${W}_{nc}$$ and $${W}_{C}$$ are the work done by non-conservation and conservative force field respectively and $$\Delta U$$ and $$\Delta K$$, be the change in P.E and K.E then
  • $${ W }_{ nc }-\Delta U=\Delta K$$
  • $${ W }_{ C }=-\Delta U$$
  • $${ W }_{ nc }+{ W }_{ C }=\Delta K$$
  • $${ W }_{ nc }=-\Delta U=-\Delta K$$
An athlete in the Olympic games covers a distance of $$100$$m in $$10$$s. His kinetic energy can be estimated to be in the range. (Assume weight = 60kg)
  • $$200J-500J$$
  • $$2\times 10^5J-3\times 10^5J$$
  • $$20000J-50000J$$
  • $$2000J-5000J$$
Work is 
  • not defined at an instant
  • not defined at a position in space
  • independent of force acting
  • a vector quantity
A man $${M}_{1}$$ of mass $$80kg$$ runs up a staircase in $$15s$$. Another man $${M}_{2}$$ also of mass $$80kg$$ runs up the stair case in $$20s$$. The ratio of the power developed by them will be:
  • $$1$$
  • $$4/3$$
  • $$16/9$$
  • None of the above
Two bodies $$A$$ and $$B$$ have masses $$20\ kg$$ and $$5\ kg$$ respectively. If they acquire the same kinetic energy. Find the ratio of thier velocities.
  • $$\dfrac {1}{2}$$
  • $$2$$
  • $$\dfrac {2}{5}$$
  • $$\dfrac {5}{6}$$
If increase in linear momentum of a body is 50%, then change in its kinetic energy is
  • 25%
  • 125%
  • 150%
  • 50%
A man displaces a block by $$5\ cm$$ on a rough surface $$(\mu=0.5)$$ by applying a force $$50\ N$$ acting at $$37^{o}$$ to the horizontal. The work done by the applied force is
  • $$200\ J$$
  • $$100\ J$$
  • $$150\ J$$
  • $$50\ J$$
A block of mass $$10kg$$ is moving in x-direction with a constant speed of $$10m/sec$$. It is subjected to a force $$F=-0.1x $$ Joules/meter during its travel from $$x=20$$ meters to $$x=30$$ meters. Its final kinetic energy will be-
  • $$475$$ joules
  • $$450$$ joules
  • $$275$$ joules
  • $$250$$ joules
The potential energy of a particle varies with position $$x$$ according to the reaction $$U(x) = 2x^{4} - 27x$$ the point $$x = 3/2$$ is point of
  • Unstable equilibrium
  • Stable equilibrium
  • Neutral equilibrium
  • None of these
A small solid sphere of mass $$m$$ is released from a point $$A$$ at a height $$h$$ above the bottom of a rough track as shown in the figure. If the sphere rolls down the track without slipping, its rotational kinetic energy when it comes to the bottom of track is
1110314_ea16297ee566408f878c33fb27d14c6f.PNG
  • $$mgh$$
  • $$\cfrac{10}{7}mgh$$
  • $$\cfrac{5}{7}mgh$$
  • $$\cfrac{2}{7}mgh$$
A worker lifts a $$20.0 kg$$ bucket of concrete from the ground up to the top of a $$20.0 m$$ tall building. What is the amount of work that the worker did in lifting the bucket?
  • $$3.92 kJ $$
  • $$400 J$$
  • $$ 560 kJ $$
  • $$ 4.08 J $$
A solid sphere of mass $$4kg$$ and radius $$1m$$ is rotating about the given axis $$xx'$$ with angular velocity $$10rad/s$$ shown in figure. The $${K.E}_{rotation}$$ is given by
1123425_c8b9d82244a24874af2191bd70723295.PNG
  • $$180J$$
  • $$200J$$
  • $$240J$$
  • $$280J$$
The average kinetic energy of an idea gas per molecule at $$25^{o}C$$, will be
  • $$6.1\times10^{-20}J$$
  • $$6.1\times10^{-21}J$$
  • $$6.1\times10^{-22}J$$
  • $$6.1\times10^{-23}J$$
Three equal resistances each of $$10\Omega  $$ are connected. The maximum power consumed by each resistor is $$20W$$. the maximum power consumed by the system is 
1131197_29ef3ab27c4846cfacc33fe9c9b94281.JPG
  • 60 W
  • 30 W
  • 15 W
  • 13.3 W
The mass of object X is $$M_1$$ and that of object Y is $$M_2$$. Keeping their kinetic energy constant, if the velocity of object Y is doubled the velocity of object X, what will be the relation between their masses?
  • $$M_1=2M_2$$
  • $$4M_1=M_2$$
  • $$M_1=4M_2$$
  • $$2M_1=M_2$$
A car weighing 1 ton is moving twice as fast as another car weighing 2 ton. The kinetic energy of the one-ton car is
  • less than that of the two-ton car is
  • some as that of the two-ton car is
  • more than that of the two-ton car is
  • impossible to compare with that of the two-ton car unless the height of each
The work function of tungsten is $$4.50eV$$. The wavelength of fastest electron emitted when light whose photon energy is $$5.50eV$$ falls on tungsten surface, is
  • $$12.27\mathring {A}$$
  • $$0.286\mathring {A}$$
  • $$12400\mathring{A}$$
  • $$1.227\mathring{A}$$
Two riffles fire the same number of bullets in a given interval of time. The second fires bullets of mass twice that fired by the first and with a velocity that is half that of the first. The ratio of their powers is?
  • $$1:4$$
  • $$4:1$$
  • $$1:2$$
  • $$2:1$$
Refer above figure.
An electric bulb 'P' rated 220 V, 60 W and, another identical bulb 'Q' is connected across the mains as shown here.
The power consumed is _ _ _ _ _

1263347_620e4d94175e4fdca57fb075f663e75c.png
  • 20W
  • 40W
  • 30W
  • 60W
A pump of $$200W$$ power is lifting $$2kg$$ water from an average depth of $$10m$$ in one second. Velocity of water delivered by the pump is :
$$(g=10m/s^2)$$
  • $$10m/s$$
  • $$2m/s$$
  • $$4 m/s$$
  • $$1 m/s$$
0:0:1


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