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CBSE Class 9 Work and Energy Important Questions have been provided in this article with detailed solutions. The questions are formulated as per the latest CBSE Board Curriculum covering all the important topics of the chapter such as work done, energy, kinetic energy, potential energy, work-energy theorem, the law of conservation of energy, etc.
Work is defined as the displacement of an object caused by a force (push or pull), whereas energy is defined as the ability to perform the work. When a force generates motion, work is completed. Energy cannot be created or destroyed; only its form may be changed. The sum of two factors determines work namely the force applied in the direction of displacement (F) and the amount of displacement of the item (s). Energy can be stored, however, that cannot be done for work. Work and Energy are both scalar quantities measured in Joules (J).
Very Short Answer Questions (1 Mark Questions)
Ques. When do we consider work is completed?
Ans. Work is considered completed when the following two conditions are met:
- The item must be affected by the force.
- The thing must be shifted.
Ques. Is the amount of work done affected by the speed with which an object is raised?
Ans. The amount of work done by an object is determined by the force used and the distance travelled. It doesn't matter how quickly you raise an object.
Ques. When riding a bicycle, what are the many energy transformations that occur?
Ans. Food's chemical energy is converted to heat, which is ultimately converted to muscle energy. Paddling converts muscular energy to mechanical energy.
Read More: Conservation Of Mechanical Energy
Ques. What is energy?
Ans. Energy refers to a person's ability to work. Energy is simply the ability to work. It's a scalar quantity with no direction and simply magnitude. Energy cannot be created or destroyed, only transformed. There are numerous forms and types of energy because they can be found in many things. Kinetic and potential energy are the most important types of energy.
Ques. What does the SI unit of work stand for?
Ans. The unit of energy in the SI system (International System of Units) is the Joule.
Ques. What relationship exists between work and energy?
Ans. Energy can be transferred in the form of force. Work is referred to the quantity of energy delivered by a force to move an item. As a result, Work and Energy have a direct relationship.
Short Answer Questions (2 Marks Questions)
Ques. In the following situations, identify the energy transformation involved:
- When a person's body is flung skyward.
- When a body is thrown from a cliff.
- When coal is consumed.
- A gas guzzler.
- Water falling from a great height.
Ans. The energy transformation involved is as follows:
- Kinetic energy into potential energy.
- Potential energy into kinetic energy.
- Chemical energy into heat energy.
- Chemical energy into heat energy.
- Potential energy into kinetic energy.
Ques. A household in a locality has consumed 250 units of energy during a month. How much energy is this in joules?
Ans. We know that 1 unit of energy is equal to 1-kilowatt hour (kWh).
1 unit = 1 kWh
Therefore, 1kWh = 3.6 × 106 J
Hence, 250 units of energy = 250 × 3.6 × 106 = 9 × 108 J.
Work Done
Ques. Is energy transferred when you push a massive rock with all your strength yet fail to move it? Where does all of your energy go?
Ans. When we push a large rock, there is no energy transfer since muscle energy is not transferred to the stationary rock. Instead, muscular energy is converted to thermal energy, causing our bodies to heat up.
Ques. When a freely falling object reaches the ground, it comes to a halt. What will happen to the kinetic energy of the object?
Ans. When an object collides with hard ground, its kinetic energy is transformed into heat and sound energy. In addition, all of the energy is lost to the environment. Depending on the nature of the ground and the quantity of kinetic energy possessed by the object, this energy can also distort it.
Ques. What is the work that gravity does on a satellite travelling around the earth? Justify your response.
Ans. Because gravity works at right angles to the direction of motion of the satellite, the work done by the force of gravity on the satellite is zero. As a result, there is no displacement in the direction of applied force. Only the direction of motion of the satellite is affected by gravity.
Ques. Ques. The bulb is powered by a battery. Explain how the process involves energy changes.
Ans. When a bulb is connected to a battery, the chemical energy in the bulb is converted to electrical energy. This electrical energy is transformed into light and heat energy when it reaches the bulb. As a result, in the given situation, the energy transition can be represented as follows:
Chemical Energy —> Electrical Energy —> Light Energy —> Heat energy
Read More: Types of Energy
Long Answer Questions (3 Marks Questions)
Ques. What are the different types of energies?
Ans. The different types of energies are as follows:
- Chemical energy is the energy released by chemical substances when they undergo a chemical reaction and are then converted into other chemicals.
- The total of potential energy and kinetic energy is known as mechanical energy.
- The movement of electrically charged particles generates electrical energy.
- Electric currents provide magnetic energy. As a result, magnetic energy refers to energy in the form of electrons.
- Nuclear energy is the energy generated during the fission or fusion processes, which is particularly useful for generating electricity.
- The movement of atoms or molecules in solids, liquids, and gases generates heat energy.
Ques. On a table, point A has a mass of 10 kg. It has been relocated to point B. What is the work done on the object by the gravitational pull if the line connecting A and B is horizontal? Explain your response.
Ans. Gravity's work is only dependent on the vertical displacement of the body. It is independent of the body's movement. As a result, gravity's work is given by:
W = mgh
Where,
Vertical displacement, h = 0
Thus, the work done by gravity on the object is given as zero joules.
Ques. State the difference between work and energy.
Ans. The difference between work and energy is as follows:
| Work | Energy |
|---|---|
| The action caused some displacement in the object. | The ability to perform work is referred to as energy. |
| Displacement is parallel to the force components. | The work that is done produces energy. |
| Work is positive if the applied force is in the same direction as the displacement. Work is negative when the applied force is in the opposite direction of the displacement. | As it is a scalar quantity, no direction component is involved. |
Potential and Kinetic Energy
Read More: Difference Between Power and Energy
Very Long Answer Questions (5 Marks Questions)
Ques. What is work?
Ans. Work completed at a given period is defined as the sum of force 'F' and displacement.
W = (F cos θ )d = F.d.
The angle produced by F and d is denoted by θ.
- When a specific amount of force is exerted externally or by the object itself to the object, work is done.
- When the angle created by force and displacement is sharp, the work done on the item is positive.
- When force and displacement are in the same direction, the work is said to be positive.
- When a force acts in the correctly angled direction of displacement (cos 90° = 0), there is zero work/no work done.
- Negative work: When the angle between force and displacement is determined to be obtuse with a degree range of 90°<θ<180°, the work done by the exerted force is enormously negative.
- Only when force and displacement are in opposite directions from one another is work done considered to be negative.
Ques. On a plough, a pair of bullocks exerts a force of 100 N. The ploughed field is 15 metres long. How much effort goes into ploughing the entire length of the field?
Ans. Force (F) = 100 N
Displacement (S) = 15 m
To Find:
Work done in ploughing the length of the field
Solution:
We know,
Work done (W) = Force (F) × Displacement (S)
⇒ W = F × S
⇒ W = 100 × 15
∴ W = 1500 J
As a result, ploughing the length of the field requires 1500 J of work.
Read More: Work Done by Gravity Formula
Ques. An object is subjected to a force of 7 N. The displacement is, say, 8 m in the force's direction. Assume that the force operates on the item by causing displacement. What work is being done in this case?
Ans. The work is completed when a force F works on an object to move it in its direction over a distance S.
Force is used to work on the body.
Work done = Force × Displacement
W = F × S
Where,
F = 7 N, S = 8 m
So, work done,
W = 7 × 8
W = 56 Nm
W = 56 J
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