Work and Energy – Short Q&A

 

Work and Energy – Short Q&A

1. Q: What is work?
   A: Work is done when a force moves an object over a distance.

2. Q: What is the formula of work?
   A: Work = Force × Distance

3. Q: In which unit is work measured?
   A: Work is measured in joules.

4. Q: What is energy?
   A: Energy is the ability to do work.

5. Q: Name two main forms of energy.
   A: Kinetic energy and potential energy.

6. Q: What is kinetic energy?
   A: Energy possessed by a moving object.

7. Q: What is potential energy?
   A: Energy stored in an object due to its position or shape.

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✅ Simple Machine – Short Q&A

8. Q: What is a machine?
   A: A machine is a tool that makes work easier.

9. Q: What is a simple machine?
   A: A simple machine is a basic device that helps us do work easily.

10. Q: Name any four simple machines.
    A: Lever, pulley, inclined plane, wheel and axle.

11. Q: What is the function of a simple machine?
    A: To make work easier by changing the direction or amount of force.

12. Q: What is the principle of a machine?
    A: Work input = Work output (Ideally)

13. Q: What is mechanical advantage?
    A: The ratio of output force to input force.

14. Q: What is efficiency of a machine?
    A: Efficiency = (Work output / Work input) × 100

15. Q: Can efficiency of a machine be 100%?
    A: No, because some energy is always lost due to friction.

16. Q: What is an actual machine?
    A: A real machine where some energy is lost as heat or sound.

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✅ Levers – Short Q&A

17. Q: What is a lever?
    A: A lever is a rigid bar that rotates around a fixed point called fulcrum.

18. Q: What is a fulcrum?
    A: The fixed point on which a lever rotates.

19. Q: What are the three parts of a lever?
    A: Fulcrum, effort, and load.

20. Q: What is the principle of a lever?
    A: Load × Load arm = Effort × Effort arm

21. Q: Name three classes of levers.
    A: First class, second class, and third class levers.

22. Q: Give one example of a first-class lever.
    A: Scissors.

23. Q: Give one example of a second-class lever.
    A: Wheelbarrow.

24. Q: Give one example of a third-class lever.
    A: Tongs.

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✅ Pulley, Wheel and Axle – Short Q&A

25. Q: What is a pulley?
    A: A pulley is a wheel with a groove used to lift loads with a rope.

26. Q: What is the function of a pulley?
    A: It changes the direction of force and helps to lift heavy objects.

27. Q: What is a wheel and axle?
    A: A wheel and axle is a simple machine made of a large wheel attached to a smaller rod (axle).

28. Q: How does a wheel and axle help?
    A: It reduces friction and makes movement easier.

29. Q: Give one example of wheel and axle.
    A: Bicycle.

30. Q: Why are simple machines useful in daily life?
    A: They save time and effort by making work easier.

A. MULTIPLE CHOICE QUESTIONS (WITH ANSWERS)

1–10: General Concepts – Work & Energy

1. Work is said to be done when:

(i) Force is applied

(ii) Force is applied and displacement occurs ✅

(iii) Only displacement occurs

(iv) No force is applied

2. SI unit of work is:

(i) Newton

(ii) Watt

(iii) Joule ✅

(iv) Erg

3. When work is done on a body, the body gains:

(i) Force

(ii) Energy ✅

(iii) Weight

(iv) Mass

4. Work done is zero when:

(i) Displacement is zero ✅

(ii) Force is applied

(iii) Motion is uniform

(iv) Force and displacement are in same direction

5. One joule of work is done when:

(i) 1 N force moves a body by 1 cm

(ii) 1 N force moves a body by 1 m ✅

(iii) 10 N moves by 10 m

(iv) 1 kg is lifted

6. Work done by gravity is:

(i) Always zero

(ii) Always positive

(iii) Positive when object falls ✅

(iv) Negative when object falls

7. Energy is the capacity to:

(i) Sit idle

(ii) Eat food

(iii) Do work ✅

(iv) Think

8. SI unit of energy is:

(i) Newton

(ii) Erg

(iii) Joule ✅

(iv) Watt

9. Kinetic energy is due to:

(i) Shape

(ii) Motion ✅

(iii) Position

(iv) Size

10. Potential energy is due to:

(i) Motion

(ii) Friction

(iii) Position or configuration ✅

(iv) Mass

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11–20: Simple Machines Basics

11. A simple machine:

(i) Reduces energy

(ii) Makes work easy ✅

(iii) Does not obey physics

(iv) Increases energy

12. A lever is a:

(i) Inclined plane

(ii) Pulley

(iii) Simple machine ✅

(iv) Compound machine

13. An inclined plane helps to:

(i) Lift objects easily ✅

(ii) Burn fuel

(iii) Increase weight

(iv) Lower gravity

14. In a machine:

(i) Load < Effort

(ii) Load = Effort

(iii) Load > Effort ✅

(iv) Load = 0

15. Mechanical advantage is:

(i) Effort ÷ Load

(ii) Load ÷ Effort ✅

(iii) Load × Effort

(iv) Load + Effort

16. Efficiency of ideal machine is:

(i) 0

(ii) 1 ✅

(iii) Less than 1

(iv) Greater than 1

17. Lever works on principle of:

(i) Pulley

(ii) Moments ✅

(iii) Tension

(iv) Gravity

18. First class lever has:

(i) Load in centre

(ii) Fulcrum in centre ✅

(iii) Effort in centre

(iv) Load and effort same

19. Examples of 1st class lever:

(i) Scissors ✅

(ii) Nutcracker

(iii) Wheelbarrow

(iv) Fishing rod

20. Pulley helps to:

(i) Increase distance

(ii) Apply force in convenient direction ✅

(iii) Do no work

(iv) Lower the load easily

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21–30: Types of Levers

21. Class I lever:

(i) Effort between fulcrum and load

(ii) Fulcrum between load and effort ✅

(iii) Load in centre

(iv) Fixed lever

22. Class II lever:

(i) Load in middle ✅

(ii) Effort in middle

(iii) Fulcrum in middle

(iv) No lever

23. Class III lever:

(i) Effort in middle ✅

(ii) Load in middle

(iii) Fulcrum in middle

(iv) Fixed fulcrum

24. Wheelbarrow is example of:

(i) 1st class lever

(ii) 2nd class lever ✅

(iii) 3rd class lever

(iv) No lever

25. Tongs are example of:

(i) 1st class lever

(ii) 2nd class lever

(iii) 3rd class lever ✅

(iv) Inclined plane

26. Mechanical advantage of lever:

(i) Load arm / Effort arm ✅

(ii) Effort arm / Load arm

(iii) Load × Effort

(iv) Load + Effort

27. A screw is a:

(i) Lever

(ii) Wedge

(iii) Inclined plane ✅

(iv) Wheel and axle

28. A wedge is used to:

(i) Lift weights

(ii) Split things ✅

(iii) Pull carts

(iv) Turn wheels

29. In pulley, effort is:

(i) Increased

(ii) Applied downward conveniently ✅

(iii) Useless

(iv) Not needed

30. A fixed pulley changes:

(i) Direction of force ✅

(ii) Magnitude of force

(iii) Energy

(iv) Distance moved

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31–40: Advanced Concepts

31. Efficiency =

(i) MA × 100

(ii) MA / VR × 100 ✅

(iii) VR / MA × 100

(iv) MA × VR × 100

32. Velocity Ratio (VR) =

(i) Load ÷ Effort

(ii) Distance moved by effort ÷ Distance moved by load ✅

(iii) Load arm / Effort arm

(iv) MA × Efficiency

33. Actual machine always has efficiency:

(i) < 1 ✅

(ii) > 1

(iii) = 1

(iv) Infinite

34. The unit of mechanical advantage is:

(i) Joule

(ii) No unit ✅

(iii) Newton

(iv) Watt

35. More friction in machine:

(i) Increases MA

(ii) Increases VR

(iii) Decreases efficiency ✅

(iv) Decreases VR

36. Scissors are examples of:

(i) 1st class lever ✅

(ii) 2nd class lever

(iii) Wedge

(iv) Pulley

37. Nut cracker is:

(i) 1st class

(ii) 2nd class ✅

(iii) 3rd class

(iv) Pulley

38. Wheel and axle increases:

(i) Speed ✅

(ii) Mass

(iii) Weight

(iv) Friction

39. A jack screw is used to:

(i) Cut

(ii) Split

(iii) Lift vehicles ✅

(iv) Turn bulbs

40. Gear system is used to:

(i) Fly

(ii) Change speed ✅

(iii) Burn fuel

(iv) Reduce energy

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41–50: Fill in the blanks (Answer only)

41. Work = Force × Displacement

42. Energy is the capacity to do Work

43. SI unit of power is Watt

44. One kilowatt = 1000 watts

45. One horsepower = 746 watts

46. Lever works on the principle of moments

47. Class I lever has fulcrum in the middle

48. Class II lever has load in the middle

49. Class III lever has effort in the middle

50. A pulley helps in changing the direction of force

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51–60: True or False

51. A machine reduces work done. – False

52. Ideal machine has no friction. – True

53. Pulley is used to lift heavy load. – True

54. Energy has no unit. – False

55. Work is done when force is applied but body doesn’t move. – False

56. Efficiency of machine is always 100%. – False

57. A screw jack is used to lift cars. – True

58. A crowbar is a class II lever. – False

59. Wedges are used in axes and knives. – True

60. Simple machines are used in daily life. – True

B. SHORT ANSWER TYPE QUESTIONS WITH ANSWERS

1. Q: When is work said to be done by a force?
   A: Work is said to be done when a force is applied on an object and the object moves in the direction of the force.

2. Q: What is energy?
   A: Energy is the capacity to do work. It is required to perform any kind of task or activity.

3. Q: What do you understand by a machine?
   A: A machine is a device that helps us do work more easily by changing the direction or magnitude of force.

4. Q: What is the principle on which a machine works?
   A: A machine works on the principle that work input is equal to work output in an ideal case (no energy loss).

5. Q: State two functions of a machine.
   A:
   (i) It makes work easier by multiplying force.
   (ii) It can change the direction of force.

6. Q: Define the term 'work input' and 'work output' in relation to a machine.
   A:

   • Work Input: The work done on the machine by applying effort.

   • Work Output: The work done by the machine on the load.

7. Q: Explain the term mechanical advantage of a machine.
   A: Mechanical advantage is the ratio of the load to the effort applied.
   Formula: M.A. = Load / Effort

8. Q: Define the term efficiency of a machine.
   A: Efficiency of a machine is the ratio of work output to work input expressed as a percentage.
   Formula: Efficiency = (Work Output / Work Input) × 100

9. Q: What is an ideal machine?
   A: An ideal machine is one in which there is no loss of energy and efficiency is 100%.

10. Q: Can a machine have an efficiency of 100%? Give a reason to support your answer.
    A: No, because some energy is always lost as heat or friction; so perfect efficiency is not possible in real machines.

11. Q: 'A machine is 75% efficient'. What do you understand by this statement?
    A: It means that 75% of the input work is converted into useful output work, and 25% is lost due to friction or other factors.

12. Q: What is a lever?
    A: A lever is a rigid bar that rotates around a fixed point called a fulcrum to lift or move loads.

13. Q: What do you mean by the mechanical advantage of a lever?
    A: It is the ratio of the load to the effort applied using a lever.

14. Q: Which class of lever has the mechanical advantage always more than 1? Give an example.
    A: Second class levers always have mechanical advantage more than 1.
    Example: Wheelbarrow.

15. Q: Which class of lever has the mechanical advantage always less than 1? Give an example.
    A: Third class levers always have mechanical advantage less than 1.
    Example: Tongs or a fishing rod.

16. Q: Give one example of class I lever in each case where the mechanical advantage is –
    (i) more than 1: Crowbar
    (ii) equal to 1: See-saw
    (iii) less than 1: Scissors

17. continued set of Short Answer Type Questions (Q.17 to Q.28) based on Simple Machines – Class VI, with clear and concise answers:

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    17. Name the class to which the following levers belong:

    Item	Class of Lever
    (a) A pair of scissors	First class lever
    (b) A lemon squeezer	Second class lever
    (c) A nut cracker	Second class lever
    (d) A pair of sugar tongs	Third class lever
    (e) A beam balance	First class lever
    (f) An oar rowing a boat	First class lever
    (g) A wheelbarrow	Second class lever
    (h) A see-saw	First class lever
    (i) A pair of pliers	First class lever
    (j) A crowbar	First class lever

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    18. The diagram given below shows the three kinds of levers. Name the class of each lever and give one example of each class.

    (a) Fulcrum in the middle
    → Class: First Class Lever
    → Example: See-saw

    (b) Load in the middle
    → Class: Second Class Lever
    → Example: Nutcracker

    (c) Effort in the middle
    → Class: Third Class Lever
    → Example: Sugar tongs

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    19. How can you increase the mechanical advantage of a lever?

    A: By increasing the length of the effort arm or reducing the length of the load arm, the mechanical advantage can be increased.

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    20. How does the friction at the fulcrum affect the mechanical advantage of a lever?

    A: Friction at the fulcrum reduces the mechanical advantage because it causes energy loss and more effort is needed.

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    21. State three differences between the three classes of levers.

    Feature	First Class	Second Class	Third Class
    Position of Fulcrum	In the middle	At one end	At one end
    Load Position	One side of fulcrum	In the middle	At the other end
    Mechanical Advantage	Can be >, = or <1	Always > 1	Always < 1
    Example	See-saw	Wheelbarrow	Tongs

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    22. What is a pulley?

    A: A pulley is a simple machine made of a wheel with a groove around it and a rope or chain passing through the groove. It is used to lift loads.

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    23. What is the mechanical advantage of an ideal pulley?

    A: The mechanical advantage of an ideal single fixed pulley is 1.

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    24. What is a screw? Give two examples.

    A: A screw is an inclined plane wound around a cylinder.
    Examples: Jar lid, screw jack.

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    25. What is a wheel and axle? Give two examples.

    A: A wheel and axle is a simple machine where a larger wheel is fixed to a smaller axle, and both rotate together.
    Examples: Door knob, bicycle.

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    26. How does a wheel help in moving the axle?

    A: When force is applied to the wheel, it turns the axle, helping to move heavy loads more easily with less force.

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    27. What is a wedge? Give two examples.

    A: A wedge is a simple machine made of two inclined planes joined together that is used to split or cut things.
    Examples: Knife, axe.

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    28. Name the machine to which the following belong:

    Item	Machine Type
    (b) Lemon crusher	Lever (Second class)

NUMERICALS

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1. In a machine, an effort of 10 kgf is applied to lift a load of 100 kgf. What is its mechanical advantage?
Solution:
$\text{Mechanical Advantage (M.A.)} = \frac{\text{Load}}{\text{Effort}} = \frac{100}{10} = \boxed{10}$

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2. The mechanical advantage of a machine is 5. How much load can it exert for an effort of 2 kgf?
Solution:
$\text{Load} = \text{M.A.} \times \text{Effort} = 5 \times 2 = \boxed{10 \text{ kgf}}$

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3. The mechanical advantage of a machine is 2. It is used to raise a load of 15 kgf. What effort is needed?
Solution:
$\text{Effort} = \frac{\text{Load}}{\text{M.A.}} = \frac{15}{2} = \boxed{7.5 \text{ kgf}}$

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4. A lever of length 100 cm has an effort of 15 kgf at a distance of 40 cm from the fulcrum at one end. What load can be applied at the other end?
Solution:
Let load arm = $100 - 40 = 60 \text{ cm}$
Using principle of moments:
$\text{Effort} \times \text{Effort arm} = \text{Load} \times \text{Load arm}$
$15 \times 40 = L \times 60 \Rightarrow 600 = 60L \Rightarrow L = \boxed{10 \text{ kgf}}$

Correction to original answer: The correct answer is 10 kgf, not 6 kgf.

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5. In a lever, the fulcrum is at one end at a distance of 30 cm from the load, and the effort is at the other end at a distance of 90 cm from the load. Find:
(a) The length of load arm
(b) The length of effort arm
(c) The mechanical advantage

Solution:
(a) Load arm = 30 cm
(b) Effort arm = 30 + 90 = 120 cm
(c)
$\text{M.A.} = \frac{\text{Effort Arm}}{\text{Load Arm}} = \frac{120}{30} = \boxed{4}$