Class 9 Physics: Work and Energy Numerical Problems

Chapter 4: Work and Energy

In Chapter 4 of Class 9 Physics, we explore the concepts of work and energy. These concepts are fundamental to understanding the behavior of objects and the transfer of energy in various systems. In this article, we will delve into the numerical problems related to work and energy, as per the NCERT textbook.

Work

Work is defined as the force applied on an object in the direction of motion. It is a scalar quantity and is given by the equation:

$$W = Fs$$

Where:

• W is work
• F is force
• s is distance

In the context of numerical problems, you may be asked to calculate the work done by a certain force on an object, given the distance over which the force is applied. For example, if a 100 N force is applied on an object that moves 10 meters, the work done is 1000 Joules.

Energy

Energy is the capacity to do work. It can be transferred from one object to another but cannot be created or destroyed. There are various forms of energy, such as potential energy, kinetic energy, and gravitational potential energy.

Potential Energy

Potential energy is the energy that an object possesses due to its position or configuration. It is given by the equation:

$$U = mgh$$

Where:

• U is potential energy
• m is mass
• g is acceleration due to gravity
• h is height

Kinetic Energy

Kinetic energy is the energy an object possesses due to its motion. It is given by the equation:

$$E = \frac{1}{2}mv^2$$

Where:

• E is kinetic energy
• m is mass
• v is velocity

Gravitational Potential Energy

Gravitational potential energy is the energy an object possesses due to its position in a gravitational field. It is given by the equation:

$$U = mgh$$

Where:

• U is gravitational potential energy
• m is mass
• g is acceleration due to gravity
• h is height

In the context of numerical problems, you may be asked to calculate the energy stored or transferred in various systems. For example, if a 100 kg object is lifted to a height of 5 meters, its potential energy is 500 Joules.

Friction

Friction is the force that opposes motion between two surfaces in contact. It is given by the equation:

$$\mu F_N$$

Where:

• μ is the coefficient of friction
• F_N is the normal force

In the context of numerical problems, you may be asked to calculate the force of friction on an object. For example, if a 1000 N force is applied on an object that moves 5 meters, the work done is 5000 Joules.

Problems

Here are some examples of problems you may encounter in the context of work and energy:

1. A 100 N force is applied on an object that moves 10 meters. Calculate the work done.
2. An object of mass 50 kg is lifted to a height of 5 meters. Calculate its potential energy.
3. A 100 kg object is moving at a velocity of 20 m/s. Calculate its kinetic energy.
4. An object is placed on a frictionless surface and a 1000 N force is applied on it. The object moves 5 meters. Calculate the work done.

These problems can be solved using the equations and concepts discussed in Chapter 4 of Class 9 Physics.