Work

1
Work

• F is the force in the direction of motion
• The object must be displaced

2
How much energy does a 60 watt light bulb consume
in one day?

• A 60 watt light bulb uses 60 joules of energy
  every second.

3
Gravitational Potential Energy

• m is the mass of the object
• g is 10 m/s2 - the acceleration due to gravity
• h is the vertical distance above an arbitrary
  zero point

4
Kinetic Energy

• m is the mass of the object
• v is the speed of the object

5
Momentum

• p is the momentum of the object-blame Newton and
  the pimento
• m is the mass of the object
• v is the velocity of the object

6
Kinetic Energy
v
m

• If we triple the velocity of the car, its kinetic
  energy will increase by a factor of 9

7
What happens to the cars kinetic energy when its
velocity is tripled?

• Therefore, the new kinetic energy is 9 times
  greater than the original kinetic energy

8
From Newtons first law of motion we know that if
the car is on frictionless ice, it cannot change

• speed
• direction

9
If we increase the velocity of a car by a factor
of 3, its K.E. will increase by a factor of 9.
How much further will the car go in stopping?

• If the frictional force backward is unchanged,
  the car must travel 9 times further while
  stopping.

10
Energy units are joules and calories

• 4.2 joules 1 calorie
• 1 Calorie 1000 calories

11
Power

• joules/sec are called watts
• 746 watts 1 horsepower

12
How much energy will a 60 watt light bulb consume
in 1 day?
13
Lets calculate the average power generated by
Miles as he runs up the stairs.

• A little over 1 horsepower

14
Conservation of energy and the roller coaster
max. G.P.E. min. K.E.
Work done to coaster
F
?X
h

• If 1,000,000 joules of work are done to the
  coaster in pulling it up the first hill, its
  total energy will always equal 1,000,000 joules-
  if no energy leaks out.

15
Conservation of energy
G.P.E. 1,000,000 joules K.E. 0 joules
G.P.E. 800,000 joules K.E. 200,0000 joules
G.P.E. 300,000 joules K.E. 700,000 joules
G.P.E. 0 joules K.E. 1,000,000 joules

• The coaster will always be moving fastest, when
  its kinetic energy is greatest

16
Can the coaster get to the top of hill D ?
A
D
B
C

• Yes, it just cannot get higher than hill A