Potential Energy
Kinetic Energy
Solving Questions & Energy Changes
Renewable & Non-Renewable Energy
Heat transfer
100
How to calculate the Gravitational Potential Energy (GPE) of an object?
GPE = m x g x h
**
m = mass
g = gravitational field strength
h = height
100
How to calculate the kinetic energy of an object?
KE = 1/2 x m x v2
100
Can a body possess energy even when it is not in motion? Explain your answer with an example.
Yes, a body possesses energy even when it is not in motion ;
Consider a body raised to a certain height say h.
Its velocity is zero. Kinetic energy will be zero but the body will have.
P.E. = mgh
Thus, a body may possess energy even though it is not in motion.
100
What is a nonrenewable resource?
A nonrenewable resource is a natural resource that cannot be re-made or re-grown at a scale comparable to its consumption.
100
What is conduction?
Conduction is the transfer of heat energy between neighbouring particles by their vibration.
200
State two factors on which the potential energy of a body at a certain height above the
ground depends.
The potential energy of a body in the raised position depends upon the following two factors:
(a) The mass of the body: Greater the mass of the body, greater is the potential energy of the
body.
(b) Its height above the ground: Higher the height of the body, greater is its potential.
200
State two factors on which the kinetic energy of a moving body depends.
The kinetic energy of a moving body depends on the following two factors :
(a) The mass of the body — Greater the mass of the body, the higher its kinetic energy.
(b)The speed of the body — The faster the speed of the body, the higher its kinetic energy.
200
A battery lights a bulb. Describe the energy changes involved in the process.
When a bulb is connected to a battery, then the chemical energy of the battery is transferred into electrical energy.
When the bulb receives this electrical energy, then it converts it into light and heat energy.
Hence, the transformation of energy in the given situation can be shown as:
200
What is renewable resources?
Renewable resources are natural resources that can be replenished in a short period.
200
Why do objects get hotter or colder?
HEAT TRANSFER FROM WARMER TO COOLER AREA
300
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 ?
A bucket full of water kept on second floor has the greater potential energy. This can be
explained as follows :
P.E. = mgh
The mass of both the bucket and the gravitational force are same, so the body at greater height will
possess more potential energy.
300
Two toy-cars A and B of masses 500 g and 200 g respectively are moving with the same speed.
Which of the two has the greater kinetic energy?
The toy car ‘A’ of mass ‘500 gm’ has the greater kinetic energy.
This can be explained as :
K.E. = 1 / 2 Mv2
Here, both the cars are moving at the same speed. So the car with greater mass will possess greater kinetic energy.
300
State the energy changes that occur in the following :
(i) Burning coal while operating a steam engine.
(ii) Lighting of a torch bulb.
(iii) An electric generator (or dynamo).
(i) Chemical energy of coal changes to heat energy of the steam. Heat energy changes into mechanical energy.
(ii) Chemical energy into light and heat energy.
(iii) Electrical energy change into mechanical energy.
300
Five examples of renewable energy are...
● Solar ● Geothermal
● Wind ● Biomass
● Water
300
The Earth is warmed by heat energy from the Sun. How does this heat energy travel from the Sun to the Earth?
There are no particles between the Sun and the Earth, so the heat cannot travel by conduction or by convection.
The heat travels to Earth by infrared waves. These are similar to light waves and can travel through space.
400
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 the greater potential energy?
Body B having a mass of 20 kg has the greater potential energy. This can be explained as follows : P.E. = mgh.
For both bodies gravity and height are the same so the body with greater mass possesses greater potential energy.
400
A cyclist doubles his speed. How will his kinetic energy change: increase, decrease or remain same?
When a cyclist doubles his speed. His kinetic energy increases four times.
K.E. = 1 / 2 Mv2
When v = doubles the K.E. quadruples
400
The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy? Why?
No. The process does not violate the law of conservation of energy. This is because when the body falls from a height, then its potential energy changes into kinetic energy progressively.
A decrease in the potential energy is equal to an increase in the kinetic energy of the body. During the process, total mechanical energy of the body remains conserved.
Therefore, the law of conservation of energy is not violated.
400
What is a renewable energy that uses plant and animal waste?
Biomass
400
A thermometer works because the liquid in it contracts when heated. This is an example of___.
Convection.
A thermometer works by measuring the expansion or contraction of a liquid, typically mercury or alcohol, in response to changes in temperature. When the liquid is heated, it expands and rises up the narrow tube of the thermometer. This movement of the liquid is an example of convection, as it involves the transfer of heat through the movement of a fluid. Convection is the process of heat transfer through the bulk movement of a fluid, such as a liquid or gas, and is different from radiation and conduction, which involve heat transfer through electromagnetic waves or direct contact, respectively.
500
An object of mass 40 kg is raised to a height of 5 m above the ground. What is its potential energy?
Gravitational potential energy is given by the expression,
GPE = mgh
Where,
h = Vertical displacement = 5 m
m = Mass of the object = 40 kg
g = Acceleration due to gravity = 9.8 m/s2
∴ GPE = 40 × 5 × 9.8 = 1960 J.
500
An object of mass 40 kg is raised to a height of 5 m above the ground. What is its potential energy?
If the object is allowed to fall, find its kinetic energy when it is halfway down.
Gravitational potential energy is given by the expression,
GPE = mgh
Where,
h = Vertical displacement = 5 m
m = Mass of the object = 40 kg
g = Acceleration due to gravity = 9.8 m/s2
∴ GPE = 40 × 5 × 9.8 = 1960 J.
At half-way down, the potential energy of the object will be 
= 980 J.
500
The kinetic energy of an object of mass, m moving with a velocity of 5 m/s is 25 J.
(i) What will be its kinetic energy when its velocity is doubled?
(i) What will be its kinetic energy when its velocity is increased three times?
Expression for kinetic energy is 1/2 mv2
m = Mass of the object
v = Velocity of the object = 5 m/s
Given that kinetic energy, KE = 25 J
(i) If the velocity of an object is doubled, then v = 5 × 2 = 10 m/s.
Therefore, its kinetic energy becomes 4 times its original value, because it is proportional to the square of the velocity. Hence, kinetic energy = 25 × 4 = 100 J.
(ii) If velocity is increased three times, then its kinetic energy becomes 9 times its original value because it is proportional to the square of the velocity. Hence, kinetic energy = 25 × 9 = 225 J.
500
What is conservation and why is it important?
Conservation means using natural resources wisely. This implies that resources should be utilized in a responsible and sustainable manner, ensuring their long-term availability for future generations. By using resources wisely, we can minimize waste, reduce environmental impact, and ensure the preservation of ecosystems. Wisely using resources also involves promoting efficiency and adopting practices that prioritize the long-term health of the planet.
500
True or False? The sun directly heats the air in our atmosphere.
False
The sun does not directly heat the air in our atmosphere. Instead, it heats the Earth's surface, which in turn warms the air through conduction and convection. The sun's rays penetrate the atmosphere and heat the land and water, causing them to release heat energy into the surrounding air. This process creates temperature variations and air currents, leading to the circulation of heat throughout the atmosphere.