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# Selina solutions Selina ICSE Concise Physics for Class 10 chapter 2 Work, Energy and Power

## Chapter 2 - Work, Energy and Power

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Define work. Is work a scalar or a vector?

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?

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 the force and displacement to get the (i) zero work (ii) maximum work?

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

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

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

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

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

In which of the following cases, is work being done?
(i) A man pushing a wall.
(ii) a coolie standing with a load of 12 kgf on his head.
(iii) A boy climbing up a staircase.

A coolie carrying a load on his head and moving on a frictionless horizontal platform does no work. Explain the reason

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

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

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

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

Express joule in terms of erg.

Differentiate between energy and power.

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

A boy of mass m climbs up a staircase 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?

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

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

Complete the following sentence:
1 J = Calorie

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

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

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

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

Differentiate between work and power.

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

What is horse power (H.P)? How is it related to the S.I. unit of power

Differentiate between watt and watt hour.

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

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MULTIPLE CHOICE TYPE:

One horse power is equal to:
(a) 1000 W
(b) 500 W
(c) 764 W
(d) 746 W

MULTIPLE CHOICE TYPE:

kWh is the unit of:
(a) power
(b) force
(c) energy
(d) none of these

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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° with the force, and (iii) normal to the force. (g = 10 N kg-1)

A boy of mass kg runs upstairs and reaches the 8 m high floor in 5 s Calculate:
the force of gravity acting on the boy.
(i) the work done by him against gravity.
(ii) the power spent by boy.
(Take g = 10 m s-2)

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

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

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.

A weight lifter 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 = 10 N kg-1

A machine raises a load of 750 N through a height of 16 m in 5 s. calculate:
(i) energy spent by machine,
(ii) power at which the machine works.

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.

A boy of mass 40 kg runs up a flight of 15 steps each 15 cm high in 10 s. Find:
(i) the work done and
(ii) the power developed by him

Take g =10 N   kg^-1

A water pump raises 50 litres of water through a height of 25 m in 5 s. Calculate the power which the pump supplies.

(Take g = 10 N kg^-1 and density of water = 1000 kg m^-3)

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

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

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What are the two forms of mechanical energy?

Name the forms of energy which a wound-up watch spring possesses.

Name the type of energy (kinetic energy K or potential energy U) possessed in the given cases:

A moving cricket ball

Name the type of energy (kinetic energy K or potential energy U) possessed in the given cases:

A compressed spring

Name the type of energy (kinetic energy K or potential energy U) possessed in the given cases:

A moving bus

Name the type of energy (kinetic energy K or potential energy U) possessed in the given cases:

The bob of a simple pendulum at its extreme position.

Name the type of energy (kinetic energy K or potential energy U) possessed in the given cases:

The bob of a simple pendulum at its mean position.

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