# Work Energy and Power Class 11 MCQ Pdf

‘work’, ‘energy’ and ‘power’ are frequently used in everyday language. In physics, however, the word ‘Work’ covers a definite and precise meaning. Energy is thus our capacity to do work. In Physics too, the term ‘energy’ is related to work in this sense, but as said above the term ‘work’ itself is defined much more precisely. The word ‘power’ is used in everyday life with different shades of meaning. In karate or boxing we talk of ‘powerful’ punches. These are delivered at a great speed. This shade of meaning is close to the meaning of the word ‘power’ used in physics.The aim of this chapter is to develop an understanding of these three physical quantities.Physical quantities like displacement, velocity, acceleration, force etc. are vectors.Work done is a scalar quantity. It can be positive or negative unlike mass and kinetic energy which are positive scalar quantities. The work done by the friction or viscous force on a moving body is negative.

## MCQs On Work Energy and Power Class 11

1. 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

2. 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) 10 J

(b) 20 J

(c) 30 J

(d) 40 J

3. A boy of mass 50 kg jumps to a height of 0.8 m from the ground then momentum transferred by the ground to boy is________________

(a) 400 kg m/s

(b) 200 kg m/s

(c) 800 kg m/s

(d) 500 kg m/s

4. A machine which is 75% efficient, uses 12 J of energy in lifting 1 kg mass through a certain distance. The mass is then allowed to fall through the same distance, the velocity at the end of its fall is___________

(a) 12 m/s

(b) 18 m/s

(c) 24 m/s

(d) 32 m/s

5. A body of mass 10 kg is displaced from point A(2, 1, 3) to point B(3, 3, 4) under the effect of a force of magnitude 20 N in the direction of 6î 8j. Calculate W.D. by the force_______

(a) 22 J

(b) 20 6 J

(c) 44 J

(d) Zero

6. 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 = 10m/s² then the power of heart in watt is____________

(a) 1.50

(b) 1.70

(c) 2.35

(d) 3.0

7. 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

8. A pump is used to deliver water at a certain rate from a given pipe. To obtain n times water from the same pipe in the same time, by what factor, the force of the motor should be increased?

(a) n times

(b) n²

times

(c) n³ times

(d) 1/n times

9. Water is falling on the blades of a turbine at a rate
of 100 kg/s from a certain spring. If the height
of the spring be 100 metres, the power transferred
to the turbine will be _________

(a) 100 kW

(b) 10 kW

(c) 30 1 kW

(d) 1000 kW

10. 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

11. A block of mass 20 kg is moved with constant velocity
along an inclined plane of inclination 37° with help
of a force of constant power 50 W. If the coefficient
of kinetic friction between block and surface is 0.25,
then what fraction of power is used against gravity?

(1)
¾

(2) ¼

(3) ½

(4) ⅛

12. Velocity of a particle of mass 1 kg moving rectilinearly is given by v = 25 – 2t + t2. Find the
average power of the force acting on the particle
between time interval t = 0 to t = 1 sec.

(a) 49 W

(b) 24.5 W

(c) –49 W

(d) –24.5 W

13. A car of mass m starts from rest and accelerates so that the instantaneous power delivered to the car has a constant magnitude P0 The instantaneous velocity of this car is proportional to________

(a) t–½

(b) t/ m

(c) t² p⁰

(d) t½

14. 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) Mg/2k

(b) Mg/k

(c) 2 Mg/k

(d) 4 Mg/k

15. A particle moves from a point ( 2î 5j) to (4j 3k) when a force of (4î 3j) N is applied.
How much work has been done by the force ?

(a) 5 J

(b) 2 J

(c) 8 J

(d) 11 J

16.What average horsepower is developed by an 80kg
man while climbing in 10 s flight of stairs that rises
6 m vertically ?

(a) 0.63 hp

(b) 1.26 hp

(c) 1.8 hp

(d) 2.1 hp

17. A body of mass m starting from rest from origin
moves along x-axis with constant power (P).Calculate relation between velocity/distance _________

(a) x ∝ v½

(b) x ∝ v 2

(c) x ∝ v

(d) x ∝ v3

18. A 1.0 hp motor pumps out water from a well of depth 20 m and fills a water tank of volume 2238
liters at a height of 10 m from the ground. The
running time of the motor to fill the empty water
tank is (g = 10m/s²
)

(a) 5 minutes

(b) 10 minutes

(c) 15 minutes

(d) 20 minutes

19. A car is moving with a speed of 40 Km/hr. If the car engine generates 7 kilowatt power, then the resistance in the path of motion of the car will be_____________

(a) 360 newton

(b) 630 newton

(c) Zero

(d) 280 newton

20. An electric motor produces a tension of 4500N
in a load lifting cable and rolls it at the rate of
2 m/s. The power of the motor is ________

(a) 9 kW

(b) 15 kW

(c) 225 kW

(d) 9 × 10³ hp

21. A body of mass 2 kg falls from a height of 20 m.What is the loss in potential energy _______

(a) 400 J

(b) 300 J

(c) 200 J

(d) 100 J

22. A projectile is fired at 300 with momentum p, neglecting friction, the change in kinetic energy, when it returns back to the ground, will be __________

(a) Zero

(b) 30 %

(c) 60 %

(d) 110%

23. A stone is projected vertically up to reach maximum height ‘h’. The ratio of its kinetic energy to potential energy, at a height 4 5 h will be _______

(a) 5 : 4

(b) 4 : 5

(c) 1 : 4

(d) 4 : 1

24. A ball of mass 1 kg is released from the tower of Pisa. The kinetic energy generated in it after falling through 10m will be _________

(a) 10 J

(b) 9·8 J

(c) 0·98 J

(d) 98 J

25. A force of 10N displaces an object by 10m. If work done is 50J then direction of force make an angle with direction of displacement ____________

(a) 120°

(b) 90°

(c) 60°

(d) None of these

26. A 2 kg mass lying on a table is displaced in the horizontal direction through 50 cm. The work done by the normal reaction will be _________

(a) 0

(b) 100 joule

(c) 100 erg

(d) 10 joule

27. A motor of 100 hp is moving a car with a constant velocity of 72 km/hour. The forward force exerted by the engine on the car is__________

(a) 3·73 × 10³ N

(b) 3·73 × 10² N

(c) 3·73 × 10¹ N

(d) none of the above

28. A crane lifts 300 kg weight from earth’s surface upto a height of 2m in 3 seconds. The average power generated by it will be____________

(a) 1960 W

(b) 2205 W

(c) 4410 W

(d) 0 W

29. 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 + t3³ where x is in metres nd t is in seconds. The work done during the first 4 second is ___________

(a) 5.28 J

(b) 450 mJ

(c) 490 mJ

(d) 530 mJ

30.If the momentum of a body is increased n times, its kinetic energy increases.

(a) n times

(b) 2n times

(c) n times

(d) n√2 times

31. If K.E. increases by 3%. Then momentum will increase by _______

(a) 1.5%

(b) 9%

(c) 3%

(d) 2%

32. If K.E. body is increased by 100%. Then % change in ‘P’.

(a) 50%

(b) 41.4%

(c) 10%

(d) 20%

33. 2 particles of mass 1 Kg and 5 kg have same momentum, calculate ratio of their K.E.

(a) 5 : 1

(b) 25 : 1

(c) 1 : 1

(d) 10 : 1

34. A machine which is 75% efficient, uses 12 J of energy in lifting 1 kg mass through a certain
distance. The mass is then allowed to fall through
the same distance, the velocity at the end of its fall is _____________

(a) √12 m/s (b) √18 m/s

(c) √24 m/s (d) √32 m/s

35. A block of mass 16 kg is moving on a frictionless
horizontal surface with velocity 4m/s and comes
to rest after pressing a spring. If the force constant of the spring is 100 N/m then the compression in the spring will be____________

(a) 3·2 m

(b) 1·6 m

(c) 0·6 m

(d) 6·1 m