Transcript Kinetic and Potential Energy

Kinetic and Potential Energy
It’s “Natural Money”
Kinetic and Potential Energy
This sum is known as the total mechanical energy of a system – in the absence of
friction this value does not change.
Kinetic and Potential Energy
Energy is most
noticeable as
it transforms
from one type
to another.
Energy Bar Charts
 A pebble is tossed up into the air.
 The simple bar charts below show how the sum of K + Ug
remains constant as the pebble rises and then falls.
© 2013 Pearson Education, Inc.
Slide 10-34
Energy Bar Charts
© 2013 Pearson Education, Inc.
Gravitational Potential Energy on a Frictionless
Surface
 The total mechanical energy
for a particle moving along
any frictionless smooth
surface is conserved,
regardless of the shape of
the surface.
© 2013 Pearson Education, Inc.
Slide 10-48
Conservation of Energy
Energy is neither created nor destroyed only changed from one form to another
To problem solve using conservation of energy use Energy initial = Energy final
*identify what type of energy is present initially
*identify what type of energy is present at the end point
© 2013 Pearson Education, Inc.
QuickCheck 10.5
Starting from rest, a marble
first rolls down a steeper hill,
then down a less steep hill of
the same height. For which is
it going faster at the bottom?
© 2013 Pearson Education, Inc.
A.
Faster at the bottom of the steeper hill.
B.
Faster at the bottom of the less steep hill.
C.
Same speed at the bottom of both hills.
D.
Can’t say without knowing the mass of the marble.
Slide 10-49
QuickCheck 10.5
Starting from rest, a marble
first rolls down a steeper hill,
then down a less steep hill of
the same height. For which is
it going faster at the bottom?
© 2013 Pearson Education, Inc.
A.
Faster at the bottom of the steeper hill.
B.
Faster at the bottom of the less steep hill.
C.
Same speed at the bottom of both hills.
D.
Can’t say without knowing the mass of the marble.
Slide 10-50
QuickCheck 10.7
Three balls are thrown from
a cliff with the same speed
but at different angles.
Which ball has the greatest
speed just before it hits the
ground?
© 2013 Pearson Education, Inc.
A.
Ball A.
B.
Ball B.
C.
Ball C.
D.
All balls have the same speed.
Slide 10-57
QuickCheck 10.7
Three balls are thrown from
a cliff with the same speed
but at different angles.
Which ball has the greatest
speed just before it hits the
ground?
© 2013 Pearson Education, Inc.
A.
Ball A.
B.
Ball B.
C.
Ball C.
D.
All balls have the same speed.
Slide 10-58
FRQ Practice
2. A roller coaster car of mass 650 kg is moving with a velocity of 15 m/s at the top of the first hill of a roller coaster track
as shown in the diagram. The cart rolls without friction down the hill and through a vertical circular loop of radius 12 m.
(a) Calculate the maximum velocity of the roller coaster.
© 2013 Pearson Education, Inc.
(b) The roller coaster travels without friction through the circular loop
i. On the diagram below, draw and label all of the forces acting on the roller coaster when it is upside down at
the top of the loop
ii Calculate the magnitude of the normal force exerted on the roller coaster when it is upside down at the top of
the loop
iii. The safety engineer determines that the acceleration of the riders is too great while they are passing through
the loop. Describe a way the engineer can modify the ride to safely reduce the acceleration of the passengers as they go
through the loop. Justify your answer.
© 2013 Pearson Education, Inc.