Science 8 Physics-Work and Energy

1. CALCULATING
WORK

2. Class Recap
If the FORCE and the OBJECT moves in
__________ direction of the force applied.
WORK IS DONE
the same

3. Class Recap
If the FORCE and the OBJECT moves in
__________ direction of the force applied.
NO WORK IS DONE
not the same

4. Class Recap
There is no movement/motion of the
force you applied.
NO WORK IS DONE

10. Example:
Suppose a woman is pushing a
grocery cart with a 500N force along
the 7 meters aisle, how much work
is done in pushing the cart from end
to end of the aisle to the other.

11. W = Fd
W = 500N (7m)
W = 3500 Nm
W = 3500 J
Solution

12. In a baseball game, Lyren
hit the ball with a force of 25
Newtons. This sent the ball
flying through 400 meters in the
midfield. How much work did
Lyren do on the ball?

13. W = Fd
W = 25N (400m)
W = 10,000 Nm
W = 10, 000 J

14. 1. A force of 500N is needed
to push a cabinet across a lot.
Two students push the cabinet
5m. How much work is done?

15. 2. Leo uses a force of 15N to
push a grocery cart a distance of 4
meters. How much work does he do?

16. 2. Leo uses a force of 15N to
push a grocery cart a distance of 4
meters. How much work does he do?

17. 3. A pail of water exerted a force
of 14N is carried to a height of 2
meters from the ground to the house,
how much work is done on the pail of
water?

18. Potential
Energy

19. Potential Energy
Stored energy due to the position of
an object. You call it potential energy
because it has the energy that is
ready to be released.

20. Potential Energy
Energy gained or lost by an object
above the ground.

22. Potential Energy
The heavier an object is, the more
gravitational potential energy it
has.
The higher an object is, the more
gravitational potential energy it
has.

27. Calculating Potential Energy
PE = mgh
mass (m)
acceleration due to gravity (g) (9.8 m/s )
height (h)
2

28. When a 1.0 kg book is lifted 0.5m from the
table, the force exerted in lifting the book is
equal to its weight. What would be the
potential energy of the book in reference from
the table?
Calculating Potential Energy

29. Calculating Potential Energy
PE = mgh
Mass = 1 kg
Gravity = 9.8 m/s
Height = 0.5 m
PE = mgh
PE = (1 kg) (9.8) (0.5)
PE = 4.9 J
2

30. A 1 kg book has a potential energy of 10J. How
high is it above the table?
PE = 10 J m = 1 kg g= h=?
Calculating Potential Energy
9.8 m/s 2

31. 1. What is the
potential energy
of a 4 kg box
lifted to 10
meters high?
2. What is the
potential energy of a
3 kg box lifted to
12.5 meters high?

34. KINETIC
ENERGY

35. Kinetic Energy
Energy of a moving
object

38. Calculating Kinetic Energy
A 3000 kg truck has a velocity
of 40 m/s. What is the truck’s
kinetic energy?

39. Calculating Kinetic Energy
A 5 kg rolling rock has a
velocity of 15 m/s. What is the
rock’s kinetic energy?

40. Factors affecting Kinetic Energy
Mass and velocity

41. Work, Energy and Power
Same mass of bag but lifts
shorter time = greater
mechanical power
Same amount of work, power
output is inversely proportional
to time.

42. Work, Energy and Power
Less time in performing the
same amount of work means
greater power output.

43. Work, Energy and Power
Same time of in lifting the bag
but bag is heavier = greater
mechanical power
Power output is directly
proportional to work

44. Work, Energy and Power
More work done for the same
amount of time means greater
power output.

45. Factors affecting Potential
Energy
Mass and height