Goyal Brothers Prakashan solutions for A New Approach to ICSE Physics [English] Class 10 chapter 2 - Work, Power and Energy [2018 edition]

State two conditions for work to be done.

State the mathematical expression for work, when a body is moving along horizontal plane.

State the mathematical expression for work, when a body is moving up an incline plane.

Name and define C.G.S. unit of work.

Name and define S.I. unit of work.

How is the S.I. unit of work related to C.G.S. unit of work?

Why is the work done by a body zero, when a force acts at right angles to the direction of displacement?

A man climbs a slope and another walks a same distance on a horizontal level road. Who does more work? Give a reason for your answer.

For the following scenario, state whether the work done by gravity is positive, negative, or zero.

A person walks on a levelled road.

For the following scenario, state whether the work done by gravity is positive, negative, or zero.

A person climbs a ladder.

For the following scenario, state whether the work done by gravity is positive, negative, or zero.

A car in neutral gear is coming down the slope.

In the following case, work is done or not done and why?

A group of boys pushing a thick wall.

In the following case, work is done or not done and why?

A porter carrying load on his head and climbing stairs.

In the following case, work is done or not done and why?

A porter carrying load on his head and walking along level road.

In the following case, work is done or not done and why?

A boy sitting on his chair and preparing his lesson.

In the following case, work is done or not done and why?

A girl swimming in a water tank.

In the following case, work is done or not done and why?

A man standing in a lift and going up to nth floor.

What is negative work?

Give two examples of negative work.

Express erg in terms of mass, length and time.

Express joule in terms of mass, length and time.

What kind of work is done when the driver of a speeding car applies brakes?

A force of 200 N acts on a body and displaces it 10 m. Calculate the work done by the force in S.I. units.

What force should an engine develop, so that it causes a displacement of vehicle through 100 m, such that work done by it is 0.50 mega joule?

A force of 1000 N is applied through a distance of 25 m while drawing a bucket of water from a well. Calculate the work done in joules.

Define power.

State two mathematical expressions for power.

Define absolute unit of power in S.I. system.

Derive the mathematical formula for the S.I. unit of power in terms of mass, length, and time.

What is horse power stating clearly where it is used?

State two factors which determine power of a body.

Name two bigger units of power in S.I. system and state their magnitude in watt.

Differentiate between work and power.

Name two smaller units of power and state their magnitude.

What do you understand by the term energy?

State the S.I. unit of energy.

State C.G.S. units of energy.

Differentiate between energy and power.

State the factors which determine the magnitude of potential energy.

Define elastic potential energy.

What is potential energy on the surface of earth?

Prove a freely swinging pendulum obeys law of conservation of energy.

What kind of energy is possessed by a body in the following case?

A stretched bow.

What kind of energy is possessed in a situation when?

A shooting arrow.

What kind of energy is possessed in a situation when?

Water stored in dams.

What kind of energy is possessed in a situation when?

A stone lying on the top of roof.

What kind of energy is possessed in a situation when?

A horse running along a level road

What kind of energy is possessed in a situation when?

An electron spinning around the nucleus.

Define kilowatt hour and convert it into joules.

Define electron volt and convert it into joules.

State the energy changes taking place in following case:

Switching on a flash light.

State the energy changes taking place in following case:

A car climbing on a steep hill road.

State the energy changes which take place when:

An air gun is loaded and then fired.

State the energy changes which take place when:

Water freezes in the freezing chamber of a fridge.

State the energy changes taking place in following case:

Exposure of a photographic film, while photographing.

State the energy changes taking place in following case:

Food consumed by human beings.

State the energy changes taking place in following case:

Burning of a strip of magnesium.

State the energy changes taking place in following case:

Water in a dam generates electricity.

State the energy changes taking place in following case:

A toy car is wound and then released.

State the energy changes taking place in following case:

Launching of a satellite by a rocket.

Give one example when:

Electric energy changes to potential energy.

Give one example when:

Potential energy changes to electric energy.

Give one example:

When magnetic energy changes into potential energy.

Give one example:

When electric energy changes into magnetic energy.

Give one example when:

Chemical energy changes to light energy.

Give one example when:

Light energy changes to chemical energy.

Give one example when:

Sound energy changes to electric energy.

Give one example when:

Electric energy changes to sound energy.

Give one example when:

Kinetic energy changes to heat energy.

Give one example when:

Heat energy changes to kinetic energy.

A machine raises a load of 750 N through a height of 16 m in 5 seconds. Calculate the power at which the machine works.

By what factor does the kinetic energy of a moving body change, when its speed is reduced by half?

What does the unit kilowatt hour measure? Define it.

From the ground floor, a man comes up to the fourth floor of building using staircase. Another person comes up the same floor using elevator. Neglecting friction compare the work done in two cases.

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

What energy changes are taking place in an oscillating pendulum?

Two objects A and B have masses in the ratio of 2 : 1 and are dropped from the same height.

1. What is the ratio of their velocities on reaching ground?
2. What is the ratio of their kinetic energy on reaching ground?

Name two different units of energy (other than S.I. unit and its multiple).

A light and heavy mass has equal momentum. Which will have more kinetic energy and why?

A, B, C and D are four points on a hemispherical cup placed inverted on the ground. Diameter BC = 360 cm and AE = `R/3` (R is the radius of the cup). A small spherical mass of 500 g at rest at the point A slides down along the smooth surface of the cup. Assuming there is no loss of energy, calculate its:

1. Potential Energy at A relative to B.
2. Speed at point B (lowest point).
3. Kinetic Energy at D (g = 10 ms⁻²).

What happens to the kinetic energy when mass of body is doubled at constant velocity?

What happens to the kinetic energy when velocity of body is doubled at constant mass?

What happens to the kinetic energy when mass of body is doubled, but velocity is reduced to half?

A boy of mass 60 kg runs upstairs in 16 s and reaches 10 m high floor. Calculate:

1. Force of gravity acting on the boy.
2. Work done by the boy against the gravity.
3. Power developed by the boy.

Name the quantity which is measured in eV.

What will be the angle between force and displacement to attain minimum work?

What will be the angle between force and displacement to attain maximum work?

The work done by the heart is 1 Joule per beat. Calculate the power of the heart if it beats 72 times in one.

State the amount of work done by an object when it moves in a circular path for one complete rotation. Give a reason to justify your answer.

Calculate the height through which a body of mass 0.5 kg is lifted if the energy spent in doing so is 1.0 J. Take g = 10 m s^-2.

When an arrow is shot from a bow, it has kinetic energy in it. Explain briefly from where does it get its kinetic energy?

A stone of mass 50 g is thrown vertically upward from the ground with the initial velocity of 20.0 ms⁻¹. Gravitational potential energy at ground level is considered zero. Apply the principle of conservation of energy to calculate the potential energy at the maximum height attained by stone. [g = 10 ms⁻¹]

6.4 kJ of energy causes a displacement of 64 m in a body in the direction of force in 2.5 seconds. Calculate:

1. Applied force.
2. Power in horse power [Take 1 HP = 750 W]

A toy car is acted upon by a force. State two conditions under which work done is zero.

A body of mass 50 kg has momentum 5000 kgms⁻¹. Calculate

1. Velocity of body
2. Kinetic energy of body.

A body of mass 0.2 kg falls from a height of 10 m to a height of 6 m above the ground. Find the loss in potential energy taking place in the body. [g = 10ms⁻²]

A moving body weighing 400 N possesses 500 J of kinetic energy. Calculate the velocity with which the body is moving. (g = 10 ms²)

Abhay exerts a force of 150 N in pulling a cart with a constant speed of 10 ms⁻¹. Calculate the power applied on cart.

Explain briefly why the work done by a fielder when he takes a catch in a cricket match is negative.

A boy drags a load 'L' along horizontal plane AB by applying a force F. The boy does:

The SI unit of work is joule. It is expressed in terms of mass, length and time as:

The SI unit of power is watt. It is expressed in terms of mass, length and time as:

A stone resting on the roof of a building has:

One horse power is equal to ______.

One electron volt is equal to ______.

Kilowatt hour is the commercial unit of ______.

Power is the product of ______.

The kinetic energy of a given body depends on the ______.

One kilocalorie is the amount of heat required to raise the temperature of:

When a flash light is switched on the electric energy:

A pendulum is swinging freely. The bob of pendulum has:

A pendulum is oscillating freely. Its bob has:

A ball of mass m is dropped from height 'h'.

The factors which determine the work done by a body are:

No work is done if the force acting on a body is:

A stone whirled around in a circle with constant speed does:

In a stretched bow and arrow system, the arrow has:

A body of mass 'm' is moving with a uniform velocity of 'v'. If the velocity increases three times the kinetic energy of the body will increase:

A glass of boiling hot water cools down to room temperature. This process of cooling is known as:

During power production in a coal-based thermoelectric power plant, the correct sequence of energy conversions taking place is:

One kilowatt hour is equal to:

A body of mass 0.2 kg falls from a height of 10 m to a height of 6 m above the ground level. If 'g' = 10 ms⁻², the loss of gravitational potential energy is:

A girl of mass 35 kg climbs from the first floor of a building at a height of 4 m above the ground to third floor at a height of 12 m above the ground. If 'g' is equal to 10 ms⁻², the increase in gravitational potential energy of the girl is:

A boy exerts a force of 150 N while pulling a hand cart at a speed of 3 ms⁻¹. The power exerted by the body is:

Assertion (A): It is not necessary that a force always causes displacement of the body in its own direction.

Reason (R): The work done depends on (i) the magnitude of force, (ii) magnitude of displacement and (iii) the angle between the force and displacement.

Assertion (A): When a coolie walks on the horizontal ground while carrying a load on his head, no work is done against the force of gravity.

Reason (R): The coolie does work against the force of friction when he moves with load.

Assertion (A): A body capable of doing work is said to possess energy.

Reason (R): There is a transfer of energy if a body is acted upon by a force normal to the direction of displacement.

Assertion (A): In the uniform circular motion, the body is acted upon by a centripetal force, normal to displacement.

Reason (R): In the uniform circular motion, work done by the body is zero.

Assertion (A): In a polyatomic molecule, atoms can vibrate about their mean positions.

Reason (R): A polyatomic molecule has the vibrational energy in addition to rotational and translational energies.

When a body vibrates about its mean position, the kinetic energy possessed by body is called ______ kinetic energy.

One watt hour is equal to ______ J.

One electron volt (eV) is equal to ______ J.

Rate of doing work is called ______.

The energy possessed by a stretched bow is ______.

Match the statements in Column A with those in Column B.

A boy of mass 55 kg runs up a flight of 40 stairs, each measuring 0.15 m in 15 s. Calculate

1. Force acting on the boy.
2. Work done by the boy.
3. Gain of potential energy by the boy.
4. Power developed by the boy.
5. Horse power and power in kilowatts.

A girl of mass 50 kg, climbs a flight of 100 stairs each measuring 0.25 m in height, in 20 s. Find

1. Force acting on the girl
2. Work done by the girl
3. Gain in potential energy
4. Power in (i) Watts (ii) Horse power.

[Take g = 10 ms⁻²; 1 HP = 750 W]

A load of 220 kg is vertically pulled up by a crane through a vertical height of 16 m in 40 s. Calculate

1. Force acting in the upward direction
2. Total work done
3. Horse power of the engine pulling the rope.

[Take g = 9.8 ms⁻²; 1 HP = 750 W]

An energy of 4 kJ causes a displacement of 64 m in 2.5 s. Calculate

1. Force
2. Power

A work of 1000 J is done on a body in 4 s, such that a displacement of 20 m is caused. Calculate

1. Force
2. Power

What force must be applied to a body through a distance of 10 m, such that it does a work of 4000 J. If the mass of body is 20 kg, what is the acceleration of the body?

An engine of power 200 W, operates for 4 s. Find the work done by the engine. If the force developed by the engine is 100 N, calculate the maximum displacement caused.

Calculate the horse power of an engine, which lifts 4000 m³ of water from a depth of 50 m in 40 minutes.

[g = 10 ms⁻², \[ \mathrm{D}_{\mathrm{H_{2}O}} \] = 10³ kg m⁻³, 1 HP = 750 W]

Calculate the horse power of the motor of an elevator, which can carry 10 persons of average mass 60 kg through a vertical height of 20 m in 30 s.

[Take g = 10 N/kg, 1 HP = 750 W]

Calculate the power of an electric pump in horse power, which can lift 2000 m³ of water from a depth of 20 m in 25 minutes.

[Take g = 10 ms⁻², 1 m³ of water = 10³ kg and 1 HP = 750 W]

Calculate the height through which a crane can lift a load of 4 t, when its motor of 4 HP operates for 10 s.

(Take g = 10 ms⁻², 1 HP = 750 W)

How long should an electric motor, of power 2 H.P. operate, so as to pump 5 m³ of water from a depth of 15m. [Take g = 10 N kg⁻¹]

An electric motor of power 200 W is switched on for 1 minute and 40 seconds. If 60% of the energy of the motor is useful, calculate

1. useful work done by the motor
2. load lifted by it through a vertical height of 10 m.

[g = 10 ms⁻²]

An electric pump is 60% efficient and is rated 2 HP. Calculate the maximum amount of water it can lift through a height of 5 m in 40 s.

[Take g = 10 ms⁻² and 1 HP = 750 W]

Calculate the time for which a motor pump of 10 HP and efficiency 80% must be switched on, so as to pump 20 m³ of water through a vertical height of 20 m.

[Density of water = 1000 kg m⁻³; g = 10 ms⁻²; 1 HP = 750 W]

In a hydroelectric power station, 1000 kg of water is allowed to drop through a height of 100 m in 1 sec. If the conversion of potential energy to electric energy is 60%. Calculate the power output. [Take: g = 10m/sec²]

A bullet of an air gun weighs 0.01 kg. It is propelled out from the air gun with a velocity of 40 ms⁻¹. Calculate the potential energy of the spring.

A compressed spring is held near a small toy car of mass 0.15 kg. On the release of the spring, the toy car moves forward with a velocity of 10 ms⁻¹. Find the potential energy of the spring.

A catapult throws a stone of mass 0.10 kg with a velocity of 30 ms⁻¹. If 25% of the P.E. of the elastic band is wasted during transmission, find the magnitude of the potential energy.

A body of mass 4 kg is moving with a velocity of 4 ms⁻¹. Find the ratio of its initial and final kinetic energy, if its mass is doubled and velocity is tripled.

A body A of mass 20 kg is moving with a velocity of 1 ms⁻¹. Another body B of mass 1 kg is moving with a velocity of 20 ms⁻¹. Find the ratio of kinetic energy of A and B.

A bullet of mass 0.2 kg, moving with a velocity of 200 ms⁻¹, strikes a stationary wooden target of mass 5 kg. If all the energy is transferred to the wooden target, calculate the velocity with which the target moves in the forward direction.

A body has a KE 'P'. If the mass of body increases 25 times, calculate its velocity, the kinetic energy remaining same.

A body of mass (m) has a velocity (v). If the mass of the body increases 81 times, but the kinetic energy remains same, calculate the new velocity.

A body P has KE (E). Another body Q, whose mass is 9 times than P, also has kinetic energy (E). Calculate the ratio of velocities of P and Q.

A force of 20 N is required to pull up a body of mass 1.5 kg through a distance of 6 m along an inclined plane as shown in diagram alongside. Calculate

1. Force of gravity acting on the body. (Take g = 10 ms⁻²)
2. Work done by the force in pulling body along the inclined plane.
3. Work done against the force due to gravity
4. Account for the difference in answers (b) and (c).

A force of 40 N is required to pull up cylindrical barrel of mass 2.5 kg through a distance of 7.5 m along the inclined plane as shown in diagram alongside. Calculate.

1. Force of gravity acting on the barrel. (Take g = 10 ms⁻²)
2. Work done by the force in pulling body along the inclined plane.
3. Work done against the force of gravity.

Adjacent diagram shows a body of mass 5 kg pulled up an inclined plane by a force of 30 N.

1. Calculate force of gravity acting on body.  (Take g = 10 ms⁻²)
2. Work done by the force in pulling body along the inclined plane.
3. Work done against the force of gravity.

A rickshaw puller exerts a force of 250 N in pulling rickshaw at a constant speed of 5 ms⁻¹. Calculate the power developed by the rickshaw puller.

A scooter develops a power of 1 HP while running at 36 km h⁻¹. Calculate the force generated by its engine.

[Take 1 HP = 750 watts]

The engine of a car develops a power of 5 HP and force 500 N while running a uniform speed S. Calculate the value of S.

The heart of running athlete is beating 100 times a minute. If the work done by the heart per beat 1.2 J, calculate the power of the heart.

The work done by the heart is 1 Joule per beat. Calculate the power of the heart if it beats 72 times in one.

The heart of a deer chased by a tiger beats 200 times in a minute and does a work of 1.4 joules per beat. What is the power of heart?

An accelerated electron has an energy of 6.4 × 10⁻¹⁹ J. Express the energy of electron in electron volts (eV).

A beam of electrons has an energy of 1 joule. How many electrons are in the beam?

[1 eV = 1.6 × 10⁻¹⁹ J]

An accelerated electron has energy of 9.6 × 10⁻¹⁸ J. Express the energy in electron volts (eV).

A body of momentum 10 kgms⁻¹ and mass 0.05 kg. Calculate the kinetic energy of body.

Calculate the kinetic energy of a body of mass 100 g and having a momentum of 20 kgms⁻¹.

Calculate the kinetic energy of a body of mass 5 kg and momentum 50 kgms⁻¹.

A lead pellet of mass 4 g leaves an air gun with a velocity of 50 ms⁻¹. What is the magnitude of potential energy stored by the spring of air gun?

A spring is kept compressed by a toy car of mass 100 g. On releasing the spring the car moves out with a speed of 0.5 ms⁻¹. Calculate the potential energy of the compressed spring.

A lead pellet of mass 10 g leaves an air gun with a velocity of 40 ms⁻¹. What is the magnitude of potential energy stored by its spring?

The given figure depicts the graph of work done vs. displacement under a constant force of 10 N. Which of the following statements is true?

A metal ball is whirled inside a ring placed on a table, as shown in the diagram P.

The diagram Q shows the motion of the ball after the ring is lifted.

Which of the following diagrams shows the correct position of the metal ball in the ring when the ring is lifted?

Assertion (A): When the displacement is zero, then the work is zero. So, if the work done is zero, then it necessarily means the displacement is zero.

Reason (R): Work done is calculated by the relation W = FS cos θ.

The mass of the block P is 5 kg. It is to be moved along an inclined plane AC of length 8 m, which makes an angle of 30° with the horizontal. A force of 50 N is applied on the block to move it through the inclined plane AC, as shown in the diagram.

1. What is the work done by the force along the inclined plane?
2. Find the gain in potential energy of block P if it is directly lifted to C from the ground. (g = 10 ms⁻²)
3. We know that potential energy is gained due to the work done on the body against gravity. Then, in this case, why is the work done on the block and the increase in the potential energy of the block different?

A ball of mass m is dropped freely from point A. It is given that AB = BC = CD = h. If the acceleration due to gravity at the given place is g, then what will be its

1. potential energy at point A?
2. kinetic energy at point C?

A block of mass 30 kg is pulled up a slope (diagram alongside) with a constant speed by applying a force of 200 N parallel to the slope. A and B are the initial and final positions of the block. Calculate the force of friction offered by the surface AB.

Shan is utilising a dynamometer to measure the force, expressed in newtons, on a bowstring. He records both the force and displacement of the bowstring and plots the data on a graph that shows the relationship between force in newtons and displacement in centimetres. Shan is interested in determining the highest point that the arrow reaches. He knows he can calculate the work done by finding the area under the graph.

1. What is the potential energy stored in the bow string, when the force is 25 N?
2. If the mass of the arrow is 31.25 g, calculate the maximum velocity attained by the arrow.
3. Calculate the maximum height reached by the arrow.

Two students are conducting experiments with identical 100 g mass simple pendulums, each raising the bob 5 m above the mean position. The graph depicting the relationship between distance from the mean position and velocities is presented in the diagram.

1. Demonstrate, using mathematical calculations, that the path followed by student 1 is devoid of friction.
2. Does the situation involving student 2 exhibit a breach of the law of conservation of energy?

In a hydraulic power station, water is first stored in a dam at a higher altitude.

1. What is the purpose of being stored at higher altitudes?
2. When the water is allowed to fall on a turbine, what change of energy takes place for the water?
3. Why is this turbine connected to the armature of a generator?
4. Which basic law of physics is followed by the whole mechanism?