Selina solutions for Concise Physics [English] Class 8 ICSE chapter 4 - Energy [Latest edition]

A coolie does no work against the force of gravity while carrying a luggage on a road.

The energy stored in water of a dam is the kinetic energy.

The energy of a flying kite is kinetic energy.

Work done by a boy depends on the time in which he does work.

Power spent by a body depends on the time for which it does work.

Work is said to be done by a forte only when ................

Work done = Force × ........................................

The energy of a body is its capacity to do .........

The S.I. unit of energy is .............

The potential energy of a body is due to its state of ................... and kinetic energy of body is due to its ...............

Gravitational potential energy U = mass × force of gravity on unit mass × ..........

Kinetic energy = 1/2 × mass × ............

Power P= ............ /time taken.

The S.I. unit of power is ..........

1 H.P. = .........

Match the following

The S.I. unit of work is

No work is done by a force if the body

Two coolies A and B do some work in time 1 minute and 2 minute respectively. The power spent is

The expression of power P is

1 H.P. is equal to

When a boy doubles his speed, his kinetic energy becomes

A boy lifts a luggage from height 2 m to 4 m. The potential energy will become

Define work.

When does a force perform work?

State two conditions when no work is done by a force.

In which of the following cases is work being done:

1. A boy pushing a heavy rock
2. A boy climbing up the stairs
3. A coolie standing with a box on his head
4. A girl moving on the road.

A coolie is moving on a road with a luggage on his head. Does he perform work against the force of gravity? Give reason for your answer.

The moon is revolving around the earth in a circular path. How much work is done by the moon?

Write the expression for work done by a force.

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

State two factors on which the work done on a body depends.

Define the term energy.

State the S.I. unit of energy.

Define 1 joule of energy.

How is work related to energy?

What are the two kinds of mechanical energy?

What is potential energy? State its unit.

Give one example of a body that has potential energy, in each of the following:

1. due to its position at a height.
2. due to its elongated stretched state.

State two factors on which the potential energy of a body at a certain height above the ground depends.

Two bodies A and B of masses 10 kg and 20 kg respectively are at the same height above the ground. Which of the two has greater potential energy?

A bucket full of water is on the first floor of your house and another identical bucket with the same quantity of water is kept on the second floor. Which of the two has greater potential energy?

Write the expression for the gravitational potential energy explaining the meaning of the symbols used.

A body of mass m is moved from ground to a height h. If the force of gravity on mass of 1 kg is g newton, find the force needed to lift the body.

A body of mass m is moved from ground to a height h. If force of gravity on mass of 1 kg is g newton, find the work done in lifting the body.

A body of mass m is moved from ground to a height h. If force of gravity on mass of 1 kg is g newton, find the potential energy stored in the body.

Define the term kinetic energy. Give one example of a body which possesses kinetic energy.

State two factors on which the kinetic energy of a moving body depends.

Two toy-cars A and Bof masses 200 g and 500 g respectively are moving with the same speed. Which of the two has greater kinetic energy?

A cyclist doubles his speed. How will his kinetic energy change: increase, decrease or remain same?

Write the expression for the kinetic energy of a body explaining the meaning of the symbols used.

A ball of mass M is moving with a speed v. What is its kinetic energy?

Name the form of energy stored in a wound up spring of a watch.

Can a body possess energy even when it is not in motion? Explain your answer with an example.

Name the type of energy (kinetic or potential) possessed by the following A moving cricket ball.

Name the type of energy (kinetic or potential) possessed by the following A stone at rest on the top of a building.

Name the type of energy (kinetic or potential) possessed by the following A compressed spring.

Name the type of energy (kinetic or potential) possessed by the following A moving bus.

Name the type of energy (kinetic or potential) possessed by the following A bullet fired from a gun.

Name the type of energy (kinetic or potential) possessed by the following Water flowing in a river.

Name the type of energy (kinetic or potential) possessed by the following  A stretched rubber band.

Give an example to show the conversion of potential energy to kinetic energy when put in use.

State the energy changes that occur in a watch spring while it unwinds.

Give reasons for the following. No work is done if a man is pushing against a wall.

Give reasons for the following Hammer drives a nail into the wood only when it is lifted up and then struck.

Give reasons for the following A horse and a dog are running with the same speed. Which one of them has more kinetic energy than the other.

Give reasons for the following A teacher moving around in the class is doing work but a child standing and reading a book is not doing any work.

State the energy changes in the following while in use An electric bulb.

State the energy changes in the following while in use An electric oven.

State the energy changes in the following while in use A loudspeaker .

State the energy changes in the following while using a microphone.

State the energy changes in the following while using an electric motor.

A force of 30 N acts on a body and moves it through a distance of 5 m in the direction of force. Calculate the work done by the force.

A man lifts a mass of 20 kg to a height of 2.5 m. Assuming that the force of gravity on 1 kg mass is 10 N, find the work done by the man.

A body, when acted upon by a force of 10 kgf, moves to a distance 0.5 m in the direction of force. Find the work done by the force. Take 1 kgf = 10 N.

Two bodies of same masses are placed at heights h and 2h. Compare their gravitational potential energy.

Find the gravitational potential energy of 2.5 kg mass kept at a height of 15 m above the ground. The force of gravity on mass 1 kg is 10 n.

The gravitational potential energy stored in a box of weight 150 kgf is 1.5 × 10⁴ J. Find the height of the box. Take 1 kgf = 10 N.

The potential energy of a body of mass 0.5 kg increases by 100 J when it is taken to the top of a tower from ground. If force of gravity on 1 kg is 10 N, what is the height of the tower?

A body of mass 60 kg is moving with a speed 50 m s_1. Find its kinetic energy.

A truck of mass 1000 kg, increases its speed from 36 km h^-1 to 72 km h^-1. Find the increase is its kinetic energy.

A car is moving with a speed of 15 km h^-1 and another identical car is moving with a speed of 30 km h^-1. Compare their kinetic energy.

A pump raises water by spending 4×10⁵J of energy in 10s. Find the power of the pump.

It takes 20 s for a girl A to climb up the stairs while girl B takes 15 s for the same job. Compare the work done .

It takes 20 s for a girl A to climb up the stairs while girl B takes 15 s for the same job. Compare the power spent by then.