Q1 Define work. When is work said to be done by a force?

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Q2 How is the work done by a force measured when
(i) force is in direction of displacement,
(ii) force is at an angle to the direction of displacement?

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Q3 A force F acts on a body and displaces it by a distance S in a direction at an angle θ with the direction of force.
(a) Write the expression for the work done by the force.
(b) What should be the angle between force and displacement so that the work done is (i) zero, (ii) maximum?


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Q4 A body is acted upon by a force. State two conditions when the work done is zero.

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Q5 State the condition when the work done by a force is (i) positive, (ii) negative. Explain with the help of examples.

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Q6 A body is moved in a direction opposite to the direction of force acting on it. State whether the work is done by the force or work is done against the force.

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Q7 When a body moves in a circular path, how much work is done by the body? Give reason

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Q8 A satellite revolves around the earth in a circular orbit. What is the work done by the satellite? Give reason.

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Q9 State whether work is done or not by writing yes or no, in the following cases?
(a) A man pushes a wall.
(b) A coolie stands with a box on his head for 15 min.
(c) A boy climbs up 20 stairs.


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Q10 A coolie X carrying a load on his head climbs up a slope and another coolie Y carrying the identical load on his head move the same distance on a frictionless horizontal platform. Who does more work? Explain the reason.

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Q11 The work done by a fielder when he takes a catch in a cricket match, is negative. Explain.

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Q12 Give an example when work done by the force of gravity acting on a body is zero even though the body gets displaced from its initial position.

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Q13 What are the S.I. and C.G.S. units of work? How are they related? Establish the relationship.

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Q14 State and define the S.I. unit of work.

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Q15 Express joule in terms of erg.

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Q16 A body of mass m falls down through a height h. Obtain an expression for the work done by the force of gravity.

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Q17 A boy of mass m climbs up a stairs of vertical height h.
(a) What is the work done by the boy against the force of gravity?
(b) What would have been the work done if he uses a lift in climbing the same vertical height?

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Q18 Define the term energy and state its S.I unit.

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Q19 What physical quantity does electron volt (eV) measure? How is it related to the S.I. unit of that quantity?

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Q20 Complete the following sentence
(a) 1 J = ..... calorie.
(b) 1 kWh = ..... J.

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Q21 Name the physical quantity which is measured in calorie. How is it related to the S.I unit of that quantity?

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Q22 Define kilowatt hour. How is it related to joule?

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Q23 Define the term power. State its S.I. unit.

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Q24 State two factors on which power spent by a source depends. Explain your answer with examples.

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Q25 Differentiate between work and power.

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Q26 Differentiate between energy and power.

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Q27 State and define the S.I unit of power.

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Q28 (a) Name the physical quantity measured in terms of horsepower.
(b) How is horsepower related to the S. I. unit of power?

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Q29 Differentiate between watt and watt-hour.

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Q30 Name the quantity which is measured in
(a) kWh
(b) kW
(c) Wh
(d) eV

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Q31 Is it possible that no transfer of energy takes place even when a force is applied to a body?

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Multiple Choice type Questions :
Q1 One horsepower is equal to
1. 1000 W
2. 500 W
3. 764 W
4. 746 W


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Q2 kWh is the unit of:
1. Power
2. Force
3. Energy
4. None of these

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Numericals :
Q1 A body, when acted upon by a force of 10 kgf, gets displaced by 0.5 m. Calculate the work done by the force, when the displacement is
(i) in the direction of force,
(ii) at an angle of 60 degree with the force, and
(iii) normal to the force where g = 10Nkg-1

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Q2 A boy of mass 40kg climbs up the stairs and reaches the roof at a height 8m in 5s. Calculate:
(i) The force of gravity acting on the boy,
(ii)The work done by him against gravity,
(iii)The power spent by the boy.
Take g = 10 ms-2

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Q3 A man spends 6.4 kJ energy in displacing a body by 64 m in the direction in which he applies force, in 2.5 s.
Calculate:
(i) the force applied and
(ii) the power spent (in H.P) by the man.

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Q4 A weight lifter lifted a load of 200 kgf to a height of 2.5 m in 5 s.
Calculate:
(i) the work done, and
(ii) the power developed by him.
Take g = 10Nkg-1

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Q5 A machine raises a load of 750N through a height of 16m in 5s. Calculate:
(i) the energy spent by the machine.
(ii) the power of the machine if it is 100% efficient.

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Q6 An electric heater of power 3 kW is used for 10 h. How much energy does it consume? Express your answer in
(i) kWh
(ii) joule.

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Q7 A water pump raises 50 litres of water through a height of 25m in 5s. Calculate the power of the pump used (assuming 100% efficiency).
(Take g = 10 N kg-1 and density of water = 1000 kg m-3).

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Q8 A pump is used to lift 500kg of water from a depth of 80m in 10s.
Calculate:
(a) The work done by the pump,
(b) The power at which the pump works, and
(c) The power rating of the pump if its efficiency is 40%. (Take g = 10m s-2).

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Q9 An ox can apply a maximum force of 1000N. It is taking part in a cart race and is able to pull the cart at a constant speed of 30ms-1 while making its best effort. Calculate the power developed by the ox.

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Q10 The power of a motor is 40 kW. At what speed can the motor raise a load of 20,000 N?

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Q11 Rajan exerts a force of 150 N in pulling a cart at a constant speed of 10ms-1. Calculate the power exerted.

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Q12 A boy weighing 350 N climbs up 30 steps, each 20 cm high in 1 minute.
Calculate:
(i) the work done, and
(ii) the power spent

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Q13 It takes 20 s for a person A of mass 50 kg to climb up the stairs, while another person B of same mass does the same in 15 s.
Compare the
(i) work done and
(ii) power developed by the persons A and B.

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Q14 A boy of weighing 40 kgf climbs up a stair of 30 steps, each 20 cm high in 4 minutes and a girl weighing 30 kgf does the same in 3 minutes.
Compare :
(i) the work done by them, and
(ii) the power developed by them. Take g = 10 N kg-1.

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Q15 A man raises a box of mass 50kg to a height of 2m in 20s, while another man raises the same box to the same height in 50s.
(a) Compare: (i) the work done, (ii) the power developed by them.
(b) Calculate the (i) the work done, (ii) the power developed by each man.
Take g = 10N kg-1

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Q16 A boy takes 3 minutes to lift a 20 litre water bucket from a 20 m deep well, while his father does it in 2 minutes.
(a) Compare:
(i) the work, and (ii) power developed by them.
(b) How much work each does?
Take density of water = 103kg m-3 and g = 9.8 N kg-1

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