Page 2 - 11-phy-4 Work and Energy

4. Work and Energy eLearn.Punjab

Learning Objectives

After studying this chapter the students will be able to:

• Understand the concept of work in terms of the product of a force and displacement in the

direction of the force.

• Understand and derive the formula Work = wd = mgh for work done in a gravitational field near

Earth’s surface.

• Understand that work can be calculated from area under the force-displacement graph.

• Relate power to work done.

• Define power as the product of force and velocity.

• Quote examples of power from everyday life.

• Explain the two types of mechanical energy.

• Understand the work-energy principle.

• Derive an expression for absolute potential energy.

• Define escape velocity.

• Understand that in a resistive medium loss of potential

energy of a body is equal to gain in kinetic energy of the

body plus work done by the body against friction.

• Give examples of conservation of energies from

everyday life. Animation 4.2: Work
• Describe some non-conventional sources of energy. Source & Credit: wikia

Work is often thought in terms of physical or mental effort. ln Physics, however, the term work
involves two things (i) force (ii) displacement. We shall begin with a simple situation in which work
is done by a constant force.

4.1 WORK DONE BY A CONSTANT FORCE

Let us consider an object which is being pulled by a constant force F at an angle q to the direction
of motion.

2 v: 1.1