CBSE Class 9 Work & Energy. Learning the important concepts is very important for every student to get better marks in examinations. The concepts should be clear which will help in faster learning. The attached concepts made as per NCERT and CBSE pattern will help the student to understand the chapter and score better marks in the examinations.

**CHAPTER 11 “Work & Energy”**

1.Work Done By A Constant Force

· Work is a scalar quantity equal to the product of the displacement x and the component of the force Fx in the direction of the displacement..

· Work is defined as a force acting upon an object to cause a displacement

· Mathematically, work can be expressed by the following equation.

· W= F x d cos q ( cos 00 = 1)

· where F = force, d = displacement, and the angle (theta) is defined as the angle between the force and the displacement vector

· Three things are necessary for the performance of work:

· There must be an applied force F.

· There must be a displacement x.

· The force must have a component along the displacement

· **N****egative work**

Force F contributes to displacement x.

**Test Yourself:**

1.Calculate Work when F= 40 N and x = 4 m.

2.Calculate Work when F = -10 N and x = 4 m.

3. A lawn mower is pushed a horizontal distance of 20 m by a force of 200 N directed at an angle of 300 with the ground. What is the work of this force?

4. A student lifts a 50 pound (lb) ball 4 feet (ft) in 5 seconds (s). How many joules of work has the student completed?

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