CBSE Class 11 Physics Work Energy and Power MCQs Set B

Question: A particle describe a horizontal circle of radius 0.5 m with uniform speed. The centripetal force acting is 10 N. The work done in describing a semicircle is
a) zero
b) 5 J
c) 5 p J
d) 10 p J
Answer: a

Question: A ball of mass m moves with speed V and strikes a wall having infinite mass and it returns with same speed, then the workdone by the ball on the wall is
a) zero
b) mvJ
c) m/v J
d) v/m J
Answer: a

Question: The engine of a vehicle delivers constant power. If the vehicle is moving up the inclined plane then, its velocity,
a) must remain constant
b) must increase
c) must decrease
d) may increase, decrease or remain same.
Answer: a

Question: A light and a heavy body have equal momentum. Which one has greater K.E.?
a) The lighter body
b) The heavier body
c) Both have equal K.E.
d) Data given is incomplete
Answer: a

Question: The potential energy of a conservative system is given by U = ay2 – by, where y represents the position of the particle and a as well as b are constants. What is the force acting on the system ?
a) – ay
b) – by
c) 2ay – b
d) b – 2ay
Answer: d

Question: A body moves a distance of 10 m along a straight line under the action of a force of 5 newtons. If the work done is 25 joules, the angle which the force makes with the direction of motion of body is
a) 0º
b) 30º
c) 60º
d) 90º
Answer: c

Question: A cord is used to lower vertically a block of mass M, a distance d at a constant downward acceleration of g/4. The work done by the cord on the block is
a) Mg d 4
b) 3Mg d 4
c) 3Mg d 4 –
d) Mg d
Answer: c

Question: A particle is taken round a circle by application of force. The work done by the force is
a) positive non–zero
b) negative non–zero
c) Zero
d) None of the options
Answer: c

Question: A boy pushes a toy box 2.0 m along the floor by means of a force of 10 N directed downward at an angle of 60º to the horizontal. The work done by the boy is
a) 6 J
b) 8 J
c) 10 J
d) 12 J
Answer: c

Question: A metallic wire of length L metre extends by l metre when stretched by suspending a weight Mg from it. The mechanical energy stored in the wire is
a) 2 Mg l
b) Mg l
c) Mg 2 l
d) Mg 4 l
Answer: c

Question: A boy carrying a box on his head is walking on a level road from one place to another is doing no work. This statement is
a) correct
b) incorrect
c) partly correct
d) cannot say
Answer: a

Question: If a force F is applied on a body and it moves with a velocity V, the power will be
a) F × v
b) F/v
c) F/v2
d) F × v2
Answer: a

Question: A small body is projected in a direction inclined at 45º to the horizontal with kinetic energy K. At the top of its flight, its kinetic energy will be
a) Zero
b) K/2
c) K/4
d) K / 2
Answer: b

Question: The speed of an object of mass m dropped from an inclined plane (frictionless), at the bottom of the plane, depends on:
a) height of the plane above the ground
b) angle of inclination of the plane
c) mass of the object
d) All of the options
Answer: a

Question: Calculate the work done on the tool by F r if this displacement is along the straight line y = x that connects these two points.
a) 2.50 J
b) 500 J
c) 50.6 J
d) 2 J
Answer: c

Question: Assertion : The work done in moving a body over a closed loop is zero for every force in nature. Reason : Work done depends on nature of force.
a) Assertion is correct, reason is correct; reason is a correct explanation for assertion.
b) Assertion is correct, reason is correct; reason is not a correct explanation for assertion
c) Assertion is correct, reason is incorrect
d) Assertion is incorrect, reason is correct.
Answer: b

Question: Calculate the work done on the tool by F r if the tool is first moved out along the x-axis to the point x = 3.00m, y = 0 and then moved parallel to the y-axis to x = 3.00m, y = 3.00
a) 67.5 J
b) 85 J
c) 102 J
d) 7.5 J
Answer: a

Question: The potential energy of a system increases if work is done
a) upon the system by a non conservative force
b) by the system against a conservative force
c) by the system against a non conservative force
d) upon the system by a conservative force
Answer: d

Question: If a shell fired from a cannon, explodes in mid air, then
a) its total kinetic energy increases
b) its total momentum increases
c) its total momentum decreases
d) None of the options
Answer: a

Question: A man pushes a wall and fails to displace it, he does
a) negative work
b) positive but not maximum work
c) no work at all
d) maximum positive work
Answer: c

Question: A particle moving in the xy plane undergoes a displacement of sr = (2iˆ +3 ˆj) while a constant force F = (5iˆ+2 ˆj) r N acts on the particle. The work done by the force F is
a) 17 joule
b) 18 joule
c) 16 joule
d) 15 joule
Answer: c

Question: No work is done if
a) displacement is zero
b) force is zero
c) force and displacement are mutually perpendicular
d) All of the options
Answer: d

Question: A particle of mass m has momentum p. Its kinetic energy will be
a) mp
b) p2m
c) p2 m
d) 2 2 p m
Answer: d

Question: When the force retards the motion of body, the work done is
a) zero
b) negative
c) positive
d) Positive or negative depending upon the magnitude of force and displacement
Answer: b

Question: A ball moves in a frictionless inclined table without slipping. The work done by the table surface on the ball is
a) positive
b) negative
c) zero
d) None of the options
Answer: c

Question: Four particles given, have same momentum. Which has maximum kinetic energy
a) Proton
b) Electron
c) Deutron
d) a-particles
Answer: b

Question: A bomb of mass 9 kg explodes into the pieces of masses 3 kg and 6 kg. The velocity of mass 3 kg is 16 m/s. The kinetic energy of mass 6 kg in joule is
a) 96
b) 384
c) 192
d) 768
Answer: c

Question: The position of a particle of mass 4 g, acted upon by a constant force is given by x = 4t2 + t, where x is in metre andt in second. The work done during the first 2 seconds is
a) 128 mJ
b) 512 mJ
c) 576 mJ
d) 144 mJ
Answer: c

Question: A body projected vertically from the earth reaches a height equal to earth’s radius before returning to the earth. The power exerted by the gravitational force is greatest
a) at the highest position of the body
b) at the instant just before the body hits the earth
c) it remains constant all through
d) at the instant just after the body is projected
Answer: b

Question: A spring of force constant 800 N/m has an extension of 5 cm. The work done in extending it from 5 cm to 15 cm is
a) 16 J
b) 8 J
c) 32 J
d) 24 J.
Answer: b

Question: A body of mass 3 kg is under a constant force which causes a displacement s in metre in it, given by the relation t2 3 s = 1 ,is in second. Work done by the force in 2 second is
a) J 8 3
b) J 3 8
c) J 5 19
d) J 19 5
Answer: b

Question: A particle moves under the effect of a force F = cx from x = 0 to x = x1, the work done in the process is
a) 2 cx1
b) 2 1 1 cx 2
c) 2 2 cx1
d) zero
Answer: b

Question: According to work-energy theorem, the work done by the net force on a particle is equal to the change in its
a) kinetic energy
b) potential energy
c) linear momentum
d) angular momentum
Answer: a

Question: A force acts on a 30 g particle in such a way that the position of the particle as a function of time is given by x = 3t – 4t2 + t3, where x is in metres and t is in seconds. The work one during the first 4 seconds is
a) 576 mJ
b) 450 mJ
c) 490 mJ
d) 530 mJ
Answer: a

Question: The work done in stretching a spring of force constant k from length l1 and l2 is
a) k( 2 ) 1 2 l 2 – l
b) k( ) 2 1 2 1 2 l 2 – l
c) k(l 2 – l1)
d) ( ) 2 k l 2 + l1
Answer: b

Question: The …X… energy V(x) of the spring is said to be zero when block and spring system is in the …Y… position. Here, X and Y refer to
a) potential, equilibrium
b) kinetic, equilibrium
c) mechanical, equilibrium
d) vibrational, left
Answer: a

Question: If the momentum of a body is increased by 50%, then the percentage increase in its kinetic energy is
a) 50%
b) 100%
c) 125%
d) 200%
Answer: c

Question: Assertion : A man rowing a boat upstream is at rest with respect to the bank. He is doing no external work. Reason : Work done by constant force, W = F s cos q.
a) Assertion is correct, reason is correct; reason is a correct explanation for assertion.
b) Assertion is correct, reason is correct; reason is not a correct explanation for assertion
c) Assertion is correct, reason is incorrect
d) Assertion is incorrect, reason is correct.
Answer: a

Question: If stretch in a spring of force constant k is tripled then the ratio of elastic potential energy in the two cases will be
a) 9 : 1
b) 1 : 6
c) 3 : 1
d) 1 : 3
Answer: a

Question: A body is moved along a straight line by a machine delivering a constant power. The distance moved by the body in time ‘t’ is proportional to
a) t3/4
b) t3/2
c) t1/4
d) t1/2
Answer: b

Question: A uniform force of (3iˆ+ ˆj) newton acts on a particle of mass 2 kg. The particle is displaced from position (2$i + k$) meter to position (4$i + 3$j – k$) meter. The work done by the force on the particle is
a) 6 J
b) 13 J
c) 15 J
d) 9 J
Answer: d

Question: A long string is stretched by 2 cm and the potential energy is V. If the spring is stretched by 10 cm, its potential energy will be
a) V / 25
b) V/5
c) 5 V
d) 25 V
Answer: d

Question: A spring of spring constant 5 × 103 N/m is stretched initially by 5 cm from the unstretched position. Then the work required to stretch it further by another 5 cm is
a) 18.75 J
b) 25.00 J
c) 6.25 J
d) 12.50 J
Answer: a

Question: Two bodies of masses 4 kg and 5 kg are moving with equal momentum. Then the ratio of their respective kinetic energies is
a) 4 : 5
b) 2 : 1
c) 1 : 3
d) 5 : 4
Answer: d

Question: One man takes 1 min. to raise a box to a height of 1 metre and another man takes 1/2 min. to do so. The energy of the
a) two is different
b) two is same
c) first is more
d) second is more
Answer: b

Question: If a motorcyclist skids and stops after covering a distance of 15 m. The stopping force acting on the motorcycle by the road is 100 N, then the work done by the motorcycle on the road is
a) 1500 J
b) –1500 J
c) 750J
d) Zero
Answer: d

Question: Kinetic energy, with any reference, must be
a) zero
b) positive
c) negative
d) both positive and negative
Answer: b

Question: A ball dropped from a height of 2m reaches to a height of 1.5m before hitting the ground. Then the percentage of potential energy lost is
a) 25
b) 30
c) 50
d) 100
Answer: a

Question: Work done by a conservative force is positive if
a) P.E. of the body increases
b) P.E. of the body decreases
c) K.E. of the body increases
d) K.E. of the body decreases
Answer: b

Question: Total ….X…. energy of a system is conserved, if the forces, doing work on it, are …..Y….. . Here, X and Y refer to
a) conservative, mechanical
b) mechanical, conservative
c) mechanical, non-conservative
d) kinetic, conservative
Answer: b