Page 2 - TRIAL 2

CHAPTER 4

Work, Energy and Power

Upon completion of these topics, students should be able to:

 Define work, energy and power
 Calculate form of energy by using formulas
 State principle of conservation of energy
 Describe conversion from one form of energy to another
 Apply the concept and formula of work, energy and power in solving the related problems
 Calculate the efficiency of mechanical

4.1 Work 7. Situation 2:
An object is placed on a horizontal smooth
1. Work is done whenever force is applied through
a distance. plane; with the force acting on it is inclined in a
certain angle, θ to the horizontal with the
2. The component of the force must be parallel to displacement.
the direction of the motion.

3. Therefore, Work, W can be defined as the F

product of the Force, F and the Displacement, s
of an object in the direction of the force. θ

Mass, m Mass, m
Work = Fs
where, s
F = the force acting

s = the displacement W = Fs
= Fxs
4. Work is a scalar quantity and its unit is the joule = (F cos θ)(s)

(J) or N m. 1 joule = 1 N m. = Fs cos θ

5. There are FIVE (5) situations to be considered in
defining the work done of an object. Example :
6. Situation 1
10 N
An object is placed on a horizontal smooth 5 kg 30°
plane, with the direction of force acting on it 0 5 kg
parallel with the displacement.
5m

W  Fs

Mass, m F Mass, m  10cos30   5
 43.30J
s

W = Fs 8. Situation 3:
Example : An object is placed on an inclined plane, with

the direction of force acting on it parallel with
the displacement.
5 kg 10 N 5 kg

5m

W = Fs = 10(5) = 50 J
1