1) The document discusses work, energy, and their relationship through the work-energy theorem. It defines work as the product of force and displacement and distinguishes between different types of work. 2) Kinetic energy and potential energy are also defined. Kinetic energy is defined as 1/2 mv^2 and potential energy as mgh. 3) The principle of conservation of energy is explained, stating that the total energy in a system remains constant, and energy can change forms but not be created or destroyed. 4) Examples are provided to demonstrate calculating work, kinetic energy, and potential energy in different scenarios. The work-energy theorem is also illustrated as showing the relationship between change in kinetic and

1. MICAELA N. ONGAN
EDESSA D. TUMACDER
BEED 4-1
WORK AND ENERGY
WORK
AND
ENERGY

2. What does work mean to you?
WORK AND ENERGY

3. Are you doing work when….
Lifting a weights?
Walking with a bag grocery in your
hand?
Completing your homework
assignment?
Writing essay?
WORK AND ENERGY

4. WORK is defined as product of the
force and displacement of an object
in the direction of force.
W = F x d
F= Force in Newton
d= Displacement in
meters.
WORK AND ENERGY

5. Atlas holds up the Earth
WORK AND ENERGY
But he doesn’t move,
dist = 0
W = F x d
He doesn’t do any work!

6. WORK AND ENERGY
When force causes a displacement, work (energy) is
positive.
When force hinders a displacement, work (energy) is
negative.
When force results in no displacement, there is no work.
Work is not a vector – but Force and displacement are.
Pushing the
rock up the hill
Pushing the rock up the
hill – but the rock keeps
rolling down
Holding the rock
steady on the hill
d
Aargh!

7. Work (J) = force (N) x distance (m)
WORK AND ENERGY
no movement
500N 500N
6m
10s
300kg
100kg
5s
Who has done the most work?

8. no movement
500N 500N
6m
10s
300kg
100kg
5s
WORK AND ENERGY
Work = 500N x
1om= 5000J
Work = 500N x 6m
=3000J

9. WORK AND ENERGY
In the picture given above F pulls a box
having 4kg mass from point A to B.
Find the work done by F.
Work done by F;
WF=F x d
=20N x 5m
=100 J

10. WORK AND ENERGY
A box having 2 kg mass, under the effect
of forces F1, F2 and F3, takes distance
5m. Which ones of the forces do work.

11. WORK AND ENERGY
Since box moves from point A to B,
only F3 does work.
W3=F3 x d
W3=30 N x 5m
=150 J

12. Try these:
• A girl pulls a sledge a distance of 100 metres.
If the force exerted by the girl is 80 newtons in
the direction in which the sledge is moving,
calculate the work done.
• A car of mass 900 kg accelerates at 3 ms-2
from rest. How much work is done after it has
travelled 100 metres?
WORK AND ENERGY

13. ENERGY• Energy is defined as CAPACITY TO DO
WORK.
SI Unit : Joule (J)
• Kinds of Energy
 Heat
 Atomic
 Electric
 Chemical
 Solar
 Nuclear
 Sound
 Mechanical
 Light
WORK AND ENERGY

14. WORK AND ENERGY

15. Forms of Energy
• KINETIC ENERGY is energy due to
the motion.
WORK AND ENERGY
Formula:
KE = ½ m
v2
Where:
m = mass (kg)
v = velocity (ms-1)SI Unit : Joule (J)
Mass, m of
F1 car in kg
Kinetic energy

16. WORK AND ENERGY
Mass= 624 kg
A 624 kg of F1 car is moving at a speed of 150
km/h. Determine the kinetic energy of the car.
Given:
• Mass = 624 kg
• Speed =
sm
s
h
km
m
h
km
/67.41
3600
1
1
1000
150 
Kinetic energy = ½ m v 2
= ½ x 624 x 41.672
= 541753.34 Joule

17. Try these:
• Determine the kinetic energy of a 625-
kg roller coaster car that is moving
with a speed of 18.3 m/s.
• Missy Reyes, the former platform
diver for the Ringling Brother's Circus,
had a kinetic energy of 12 000 J just
prior to hitting the bucket of water. If
Missy's mass is 40 kg, then what is
her speed?
• A 300 kg car has a kinetic energy of
500 J. Find its speed.
WORK AND ENERGY

18. WORK AND ENERGY
POTENTIAL ENERGY is
energy possessed by an object due
to its position or state.
Formula:
PE = m g h Where:
m= mass (kg)
g = gravitational
acceleration (ms-1)
h = height (m)
SI Unit : Joule (J)
The cat has a
POTENTIAL ENERGY
at high position.

19. A load with as mass 5 kg was lifted up
by a pulley to the height of 0.8 m for pile
work. (Use, g = 9.81 m/s2). What is
Potential Energy the load.
WORK AND ENERGY
Solution
PE = m g h
= 5 kg ( 9.81 m/s2) ( 0.8m)
= 39.24 J

20. Try these:
• A 50 kilogram object is located 5
meters above the ground level. Find
its potential energy.
• A 12 kg cat who is resting on a tree
has a potential energy of 50 J.
Calculate its position (height)
relative to the ground.
• A girl runs up a 5 meter high flight of
stairs and she has 1000 J of
potential energy at the top.
Calculate her mass.
WORK AND ENERGY

21. The principle of conservative of
energy states that:
1) Energy cannot be created
and
destroyed
2) Energy can change from one
form to another form.
3) Total of energy is constant.
WORK AND ENERGY
Principle of Conservation of Energy

22. WORK AND ENERGY
How energy transform from
one form to another form?

23. WORK AND ENERGY
Total energy is constant.

24. WORK AND ENERGY
Energy is neither
created nor destroyed.
It can be transferred from one
object to another or transformed
from one form to another.
Law of conservation of
energy.

25. WORK AND ENERGY
Work-Energy Theorem
• Newton’s 2nd law: F=m a
Work= change in ½mv2

26. WORK AND ENERGY
Kinetic Energy = ½mv2
kg m2
s2
work = F x dist∥
N m =kg m
s2
m
same!
=1Joule

27. WORK AND ENERGY
start
dist dist∥
W=mg
Work = F x dist∥
= -mg x change in height
= -change in mg h

28. WORK AND ENERGY
Gravitational Potential Energy
Workgrav = -change in mgh
This is called:
“Gravitational Potential
Energy” (or PEgrav)
change in PEgrav = -Workgrav

29. WORK AND ENERGY
If gravity is the only force
doing work….
Work-energy theorem:
-change in mgh = change in ½ mv2
0 = change in mgh + change in ½ mv2
change in (mgh + ½ mv2) = 0
mgh + ½ mv2 = constant

30. WORK AND ENERGY
Conservation of energy
mgh + ½ mv2 = constant
Gravitational
Potential energy
Kinetic energy
If gravity is the only force that does work:
PE + KE = constant
Energy is conserved

31. WORK AND ENERGY
Example: A rocket of mass
1.5x104 kg accelerates at 220m/s2
for 29s from an initial speed of
5200m/s. (a) How fast will be rocket
be travelling after the 29s? (b) How
much Kinetic Energy has the rocket
gained?
t = time = 29s
a = acceleration = 220m/s2
v = final speed = ?
u = initial speed = 5200m/s

32. WORK AND ENERGY
Solution:
a= v -u / t
v – u = at
v = u + at
= 5200 + (220 x 29)
= 5200 + 6380
v = 11580m/s

33. WORK AND ENERGY
(b) How much Kinetic Energy has the
rocket gained?
Solution: Calculate the kinetic energy of
the rocket both before and after the
acceleration and work out the
difference.
Initial Kinetic Energy:
KE = 1 2 mv2
=0.5 x (1.5x104 ) x
(5200)2 =2.028 x 1011J

34. WORK AND ENERGY

35. WORK AND ENERGY
A lump of ice falls from an
aeroplane as it comes in to land. If
the ice hits the ground with a
vertical speed of 85m/s, what was
the height of the plane when the
ice fell off? (Assume that friction
can be ignored.)
ASSIGNMENT:

36. References:
• http://lc.brooklyn.cuny.edu/smarttutor/corc1331/PotEn.html
• http://www.physicsclassroom.com/class/energy/Lesson-
1/Kinetic-Energy
• http://www.seai.ie/Schools/Post_Primary/Subjects/Physics/Uni
t_
• 1_-_Work/Sample_questions/
• http://mrmackenzie.co.uk/wp-
content/uploads/2007/02/examples-of-kinetic-energy-
problems.pdf
• http://www.slideshare.net/smartgeniusproduction/work-
energy-and-power-ppt?from_action=save
• http://image.slidesharecdn.com/destructforcessponge-
120208152131-phpapp02/95/destruct-forces-worksheet-1-
728.jpg?cb=1361666018
WORK AND ENERGY

37. THE END...
WORK AND ENERGY