CBSE Class 11 Physics Work Energy Power Assignment

Question. The vector sum of two forces is perpendicular to their vector differences. In that case, the forces
(a) are equal to each other
(b) are equal to each other in magnitude
(c) are not equal to each other in magnitude
(d) cannot be predicted.
Answer. B

Question. Consider a drop of rain water having mass 1 g falling from a height of 1 km. It hits the ground with a speed of 50 m s^–1. Take g constant with a value 10 m s^–2.
The work done by the
(i) gravitational force and the
(ii) resistive force of air is
(a) (i) 1.25 J (ii) –8.25 J
(b) (i) 100 J (ii) 8.75 J
(c) (i) 10 J (ii) –8.75 J
(d) (i) –10 J (ii) –8.25 J 
Answer. C

Question. A particle of mass 10 g moves along a circle of radius 6.4 cm with a constant tangential acceleration. What is the magnitude of this acceleration if the kinetic energy of the particle becomes equal to 8 × 10^–4 J by the end of the second revolution after the beginning of the motion?
(a) 0.18 m/s²
(b) 0.2 m/s²
(c) 0.1 m/s²
(d) 0.15 m/s²
Answer. C

Question. A bullet of mass 10 g leaves a rifle at an initial velocity of 1000 m/s and strikes the earth at the same level with a velocity of 500 m/s. The work done in joule for overcoming the resistance of air will be
(a) 375
(b) 3750
(c) 5000
(d) 500
Answer. B

Question. A body moves a distance of 10 m along a straight line under the action of a 5 N force. If the work done is 25 J, then angle between the force and direction of motion of the body is
(a) 60°
(b) 75°
(c) 30°
(d) 45° 
Answer. A

Question. When a body moves with a constant speed along a circle
(a) no work is done on it
(b) no acceleration is produced in it
(c) its velocity remains constant
(d) no force acts on it.
Answer. A

Question. A particle of mass 5m at rest suddenly breaks on its own into three fragments. Two fragments of mass m each move along mutually perpendicular directionwith speed v each. The energy released during the process is
(a) 3/5 mv²
(b) 5/3 mv²
(c) 3/2 mv²
(d) 4/3 mv²
Answer. D

Question. A body of mass (4m) is lying in x-y plane at rest.It suddenly explodes into three pieces. Two pieces, each of mass (m) move perpendicular to each other with equal speeds (v). The total kinetic energy generated due to explosion is
(a) mv²
(b) 3/2 mv²
(c) 2mv²
(d) 4mv²
Answer. B

Question. An engine pumps water continuously through a hose. Water leaves the hose with a velocity v and m is the mass per unit length of the water jet. What is the rate at which kinetic energy is imparted to water?
(a) mv³
(b) 1/2 mv²
(c) 1/2 m²v²
(d) 1/2 mv³
Answer. D

Question. A shell of mass 200 gm is ejected from a gun of mass 4 kg by an explosion that generates 1.05 kJ of energy.
The initial velocity of the shell is
(a) 40 m s^–1
(b) 120 m s^–1
(c) 100 m s^–1
(d) 80 m s^–1
Answer. C

Question. A bomb of mass 30 kg at rest explodes into two pieces of masses 18 kg and 12 kg. The velocity of 18 kg mass is 6 m s^–1. The kinetic energy of the other mass is
(a) 324 J
(b) 486 J
(c) 256 J
(d) 524 J.
Answer. B

Question. A ball of mass 2 kg and another of mass 4 kg are dropped together from a 60 feet tall building. After a fall of 30 feet each towards earth, their respective kinetic energies will be in the ratio of
(a) 2 :1
(b) 1 : 4
(c) 1 : 2
(d) 1: 2 
Answer. C

Question. A stationary particle explodes into two particles of masses m₁ and m₂ which move in opposite directions with velocities v₁ and v₂. The ratio of their kinetic energies E₁/E₂ is
(a) m₂/m₁
(b) m₁/m₂
(c) 1
(d) m₁v2/m₂v₁
Answer. A

Question. If kinetic energy of a body is increased by 300% then percentage change in momentum will be
(a) 100%
(b) 150%
(c) 265%
(d) 73.2%.
Answer. A

Question. A particle is projected making an angle of 45° with horizontal having kinetic energy K. The kinetic energy at highest point will be
(a) K/√2
(b) K/2
(c) 2K
(d) K
Answer. B

Question. Two bodies with kinetic energies in the ratio of 4 : 1 are moving with equal linear momentum. The ratio of their masses is
(a) 4 : 1
(b) 1 : 1
(c) 1 : 2
(d) 1 : 4
Answer. D

Question. Two bodies of masses m and 4m are moving with equal kinetic energies. The ratio of their linear momenta is
(a) 1 : 2
(b) 1 : 4
(c) 4 : 1
(d) 1 : 1
Answer. A

Question. The kinetic energy acquired by a mass m in travelling distance d, starting from rest, under the action of a constant force is directly proportional to
(a) m
(b) m⁰
(c) m
(d) 1 √m
Answer. B

Question. Two masses of 1 g and 9 g are moving with equal kinetic energies. The ratio of the magnitudes of their respective linear momenta is
(a) 1 : 9
(b) 9 : 1
(c) 1 : 3
(d) 3 : 1 
Answer. C

Question. A particle of mass M is moving in a horizontal circle of radius R with uniform speed v. When it moves from one point to a diametrically opposite point, its
(a) kinetic energy change by Mv²/4
(b) momentum does not change
(c) momentum change by 2Mv
(d) kinetic energy changes by Mv²
Answer. C

Question. A force F = 20 + 10y acts on a particle in y-direction where F is in newton and y in meter. Work done by this force to move the particle from y = 0 to y = 1 m is
(a) 20 J
(b) 30 J
(c) 5 J
(d) 25 J
Answer. D

Question. A force acts on a 3 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 done during the first 4 second is
(a) 490 mJ
(b) 450 mJ
(c) 240 mJ
(d) 530 mJ
Answer. C

Question. A position dependent force,F = (7 – 2x + 3x²) N acts on a small body of mass 2 kg and displaces it from x = 0 to x = 5 m. The work done in joule is
(a) 135
(b) 270
(c) 35
(d) 70
Answer. A

Question. The potential energy of a system increases if work is done
(a) upon the system by a nonconservative force
(b) by the system against a conservative force
(c) by the system against a nonconservative force
(d) upon the system by a conservative force.
Answer. B

Question. A mass m is attached to a thin wire and whirled in a vertical circle. The wire is most likely to break when
(a) inclined at an angle of 60° from vertical
(b) the mass is at the highest point
(c) the wire is horizontal
(d) the mass is at the lowest point
Answer. D

Question. A particle with total energy E is moving in a potential energy region U(x). Motion of the particle is restricted to the region when
(a) U(x) < E
(b) U(x) = 0
(c) U(x) ≤ E
(d) U(x) > E
Answer. C

Question. A child is sitting on a swing. Its minimum and maximum heights from the ground 0.75 m and 2 m respectively, its maximum speed will be
(a) 10 m/s
(b) 5 m/s
(c) 8 m/s
(d) 15 m/s
Answer. B

Question. A block of mass M is attached to the lower end of a vertical spring. The spring is hung from a ceiling and has force constant value k. The mass is released from rest with the spring initially unstretched. The maximum extension produced in the length of the spring will be
(a) 2Mg/k
(b) 4Mg/k
(c) Mg/2k
(d) Mg/k
Answer. A

Question. The potential energy of a long spring when stretched by 2 cm is U. If the spring is stretched by 8 cm the potential energy stored in it is
(a) U/4
(b) 4U
(c) 8U
(d) 16U
Answer. D

Question. When a long spring is stretched by 2 cm, its potential energy is U. If the spring is stretched by 10 cm, the potential energy stored in it will be
(a) U/5
(b) 5U
(c) 10U
(d) 25U 
Answer. D

Question. Two springs A and B having spring constant KA and KB (KA = 2KB) are stretched by applying force of equal magnitude. If energy stored in spring A is EA then energy stored in B will be
(a) 2EA
(b) EA/4
(c) EA/2
(d) 4EA
Answer. A

Question. A body of mass 1 kg is thrown upwards with a velocity 20 m/s. It momentarily comes to rest after attaining a height of 18 m. How much energy is lost due to air friction? (g = 10 m/s²)
(a) 30 J
(b) 40 J
(c) 10 J
(d) 20 J
Answer. D

Question. 300 J of work is done in sliding a 2 kg block up an inclined plane of height 10 m. Work done against friction is (Take g = 10 m/s²)
(a) 1000 J
(b) 200 J
(c) 100 J
(d) zero.
Answer. C

Question. The heart of a man pumps 5 litres of blood through the arteries per minute at a pressure of 150 mm of mercury.
If the density of mercury be 13.6 × 10³ kg/m³ and g = 10 m/s² then the power (in watt) is
(a) 3.0
(b) 1.50
(c) 1.70
(d) 2.35 
Answer. C

Question. One coolie takes 1 minute to raise a suitcase through a height of 2 m but the second coolie takes 30 s to raise the same suitcase to the same height. The powers of two coolies are in the ratio
(a) 1 : 3
(b) 2 : 1
(c) 3 : 1
(d) 1 : 2
Answer. D

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. An engine pumps water through a hose pipe. Water passes through the pipe and leaves it with a velocity of 2 m/s. The mass per unit length of water in the pipe is 100 kg/m. What is the power of the engine?
(a) 400 W
(b) 200 W
(c) 100 W
(d) 800 W
Answer. D

Question. Water falls from a height of 60 m at the rate of 15 kg/s to operate a turbine. The losses due to frictional forces are 10% of energy. How much power is generated by the turbine ? (g = 10 m/s²)
(a) 12.3 kW
(b) 7.0 kW
(c) 8.1 kW
(d) 10.2 kW
Answer. C

Question. Body A of mass 4m moving with speed u collides with another body B of mass 2m, at rest. The collision is head on and elastic in nature. After the collision the fraction of energy lost by the colliding body A is
(a) 5/9
(b) 1/9
(c) 8/9
(d) 4/9
Answer. C

Question. A moving block having mass m, collides with another stationary block having mass 4m. The lighter block comes to rest after collision. When the initial velocity of the lighter block is v, then the value of coefficient of restitution (e) will be
(a) 0.5
(b) 0.25
(c) 0.8
(d) 0.4
Answer. B

Question. A bullet of mass 10 g moving horizontally with a velocity of 400 m s^–1 strikes a wooden block of mass 2 kg which is suspended by light inextensible string of length 5 m. As a result, the centre of gravity of the block is found to rise a vertical distance of 10 cm. The speed of the bullet after it emerges out horizontally from the block will be
(a) 100 m s^–1
(b) 80 m s^–1
(c) 120 ms^–1
(d) 160 m s^–1
Answer. C

Question. Two identical balls A and B having velocities of 0.5 m s^–1 and –0.3 m s^–1 respectively collide elastically in one dimension. The velocities of B and A after the collision respectively will be
(a) –0.5 m s^–1 and 0.3 m s^–1
(b) 0.5 m s^–1 and –0.3 m s^–1
(c) –0.3 m s^–1 and 0.5 m s^–1
(d) 0.3 m s^–1 and 0.5 m s^{–1
Answer. B}

Question. A metal ball of mass 2 kg moving with speed of 36 km/h has a head on collision with a stationary ball of mass 3 kg. If after collision, both the balls move as a single mass, then the loss in K.E. due to collision is
(a) 100 J
(b) 140 J
(c) 40 J
(d) 60 J. 
Answer. D

Question. A moving body of mass m and velocity 3 km/hour collides with a body at rest of mass 2m and sticks to it. Now the combined mass starts to move. What will be the combined velocity?
(a) 3 km/hour
(b) 4 km/hour
(c) 1 km/hour
(d) 2 km/hour
Answer. A