B.
Set
Hill 1
to 75 cm and the other hills to 0 cm. What is the height in meters?
C.
What is the potential energy of the car, in joules?
7.
Calculate
: Kinetic energy (
K
) depends on the mass and speed (
v
) of the object. The
equation for kinetic energy is:
K
=
mv
With
Hill 1
set to 75 cm, click
Play
and allow the car to reach the bottom.
A.
What is the final speed of the car, in meters per second?
B.
What is the kinetic energy of the car, in joules? (Use the mass in kg.)
C.
How does the car’s kinetic energy at the bottom of the hill compare to its potential
energy at the top?
8.
Challenge
: With no friction, you can use the relationship between potential and kinetic
energy to predict the speed of the car at the bottom of this hill from its starting height. To do
this, start by setting the kinetic and potential energy equations equal to one another:
K
=
mv
2
=
mgh
A.
Use algebra to solve for the speed.
v
2
U
=

B.
With no friction, does the final speed depend on the mass of the car?
C.
With no friction, does the final speed depend on the steepness of the hill?
D.
What is the final speed of the car if the height of the hill is 55 cm (0.55 m)?
Use the Gizmo to check your answer.
Activity C:
Breaking the egg
Get the Gizmo ready
:
·
Click
Reset
·
Check that the
Coefficient of friction
is
0.00.
Introduction:
As the car rolls down a hill, it speeds up, gaining kinetic energy. The car also
gains
momentum
. The magnitude of an object’s momentum (
p
) can be found by multiplying the
mass and speed (
p
=
mv
).
Question: What determines whether the car will break the egg?
1.
Form hypothesis
: Which factor(s) do you think determine whether the car breaks the
egg?
.

ÿ
The speed of the car only
ÿ
The momentum of the car
ÿ
The kinetic energy of the car
2.
Collect data
: Use the Gizmo to find the
minimum
hill height at which each car breaks the
egg. In the table below, fill in the hill height (in centimeters and meters), and the speed of the
car (in cm/s and m/s). Leave the last two columns blank for now.
Car
mass
(kg)
Heigh
t (cm)
Heig
ht
(m)
Spee
d
(cm/
s)
Spe
ed
(m/s
)
Momentu
m
(kg•m/s)
Kineti
c
energ
y (J)
0.035
kg
0.050
kg
0.100
kg
3.
Analyze
: Using the equations
p
=
mv
and
K
=
mv
2
, calculate the momentum and kinetic
energy of each car. Remember to use the kg and m/s values for each calculation. Fill in the
last two columns of the table.
A.
Does the car’s mass alone determine whether the egg breaks?
B.
Does the car’s speed alone determine whether the egg breaks?
C.
Does the car’s momentum determine whether the egg breaks?

D.
Does the car’s kinetic energy determine whether the egg breaks?
Explain your answers:
Draw conclusions
: What is the minimum energy required to break the egg?