®
S p r i n g C a r t L a u n c h e r
T r a d i t i o n a l E x p e r i m e n t
6
8.
Use the value of
k
that you found in the previous part and Equation 3 to calculate
U
spring
.
9.
Look at the graph of velocity versus time to find the velocity of the cart just after
the launch.
10.
Measure the mass of the cart with the launcher and spring attached.
11.
Use Equation 4 to calculate the kinetic energy of the cart.
12.
Compare the initial potential energy of the spring to the kinetic energy of the cart.
Are they equal? If not, what might account for the difference?
Traditional Experiment
In this experiment (which does not require sensors), you will determine the spring
constant by using a hanging mass to apply a known force. To determine the energy
transferred to the cart, you will observe the maximum height that the cart reaches as it
runs up an inclined track.
Spring Constant
1.
Follow set-up steps 1
through 3 on page 2.
2.
Install an end stop about 20 cm from the end of the track.
3.
Clamp a pulley to the same end of the track.
4.
Position the track so that a mass hanging from the pulley is free to hang over the
edge of your lab bench.
5.
Level the track so that the cart does not roll when release from a standstill.
6.
Place the cart on the track with the launcher shaft through the hole in the end
stop.
7.
Tie a piece of string (about 40 cm long) to the launcher shaft. Run the string over
the pulley and hang a 100 g mass from the string.
8.
Adjust the pulley so that the string is horizontal between the pulley and the
launcher shaft.
9.
In a table, record the position of the cart on the track and the total mass hanging
from the string.
10.
Add 100 g to the hanging mass.
11.
Repeat steps 9 and 10 up to about 500 g.
12.
Calculate the force applied to the spring at each step:
F
x
=
m
h
g
, where
m
h
is the
hanging mass and
g
= 9.8 m/s
2
.
13.
Make a graph of
F
x
versus cart position.
14.
Draw a best-fit line on your graph. The slope of that line equals the spring con-
stant,
k
.
