Work & Energy
Name: _____________________
Class: _____________________
Pre-Lab Questions Page
Roster Number: _____________
Instructor: __________________
1. List the equation that represents the relationship between Work and Kinetic Energy.
2. List two possible units for Work and Kinetic Energy.
3. Verify that the units for Kinetic Energy ( K.E. = ½ m v2 ) is Nm.
4. A mass, m, is held at rest, and then dropped. Using the Work-Energy theorem, find the velocity
of the mass after it has fallen 3 meters.
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WORK AND ENERGY
OBJECTIVE: Explore the relationship between work and kinetic energy. Verify the WorkEnergy theorem by experimentally determining the work done on a glider by a launcher.
APPARATUS:
Air track with ULI timer(photo gate)
Glider
Balance
Cord
Logger Pro timer software
metal block
Figure 1 (Kinetic Energy)
INTRODUCTION:
When net work is done on an object, energy is provided to that object in the form of kinetic
energy. Work done on an object by a force is defined to be the product of that force that is
parallel to the objects displacement and the displacement itself.
W = F|| ∙ d
Eq. 1
where F|| is any force or component of a force that is parallel to the objects displacement, and d is
the displacement of the object while the force is applied.
2
A more general form of the equation for Work is the following:
W = F d cos 
Eq. 2
Where F is the force on the object, d is the displacement of the object, and  is the angle between
the force vector and the displacement. The S.I. units for work is Nm or J (Joules).
The amount of energy supplied by the force doing the work is given to (or taken from) the object
in the form of kinetic (moving) energy. This leads to the work energy theorem:
Wnet = Final Kinetic Energy - Initial Kinetic Energy
Kinetic Energy is given by the following equation:
K.E. = ½ m v2
Eq. 3
Therefore the Work-Energy Theorem can be written as:
Wnet = K.E.f - K.E.o
Eq. 4
In this experiment you will comparing the work done on a glider by gravity to the kinetic energy
gained by the glider. A glider will start from rest, slide down an inclined air track and pass
through a photogate.
The computer data will allow you to find the kinetic energy of the glider when it passes through
the photogate. You will calculate the work done by gravity on the glider, and then compare this
with the final kinetic energy of the glider.
PROCEDURE : Kinetic Energy
1.
(Check out the Vernier Caliper from the instructor.) Measure and record the flag
length. Measure and record the mass of the glider and flag. Measure and record the
thickness of the metal block. Place the metal block under one leg of the air track.
Measure the distance between the legs (double legs and single leg of the air track) using
the tape measure glued to the air track
2.
Turn on the computer and then click on the Physics Lab folder and select the WorkEnergy-CP template. Reading the instructions in the text window-click on the <Set up>
menu, then select <data collection>, and <sampling>. Enter the flag length in the
appropriate units. Now click <OK>.
3.
Click on the <COLLECT> button and then release the glider from rest 100cm in front of the
photogate. When the glider passes through the photo gate, a table of your data should
appear on the screen.
4.
Repeat step three four more times so you have a total of 5 similar speeds.
5.
After all five runs have been completed, click the
looks reasonable.
3
STOP
button. Save this data if it
CALCULATIONS:
1.
Calculate the angle of the air track. Using the thickness of the metal block and the length
between the legs of the air track, construct a right triangle.
2.
Calculate the average speed of the five runs. Using Equation 3, find the kinetic energy of
the glider when it entered the air track.
3.
Draw a free body diagram for the mass on the air track. Using this, the angle you figured
earlier, the 100 cm displacement of the glider, and equation 2, find:
a) the work done by gravity
b) the work done by the normal force
4.
To verify equation 4, find the percent difference between the kinetic energy attained by the
glider and the work done by gravity.
4