Investigating the Conservation of Energy - Physics A
If a cart starts rolling down an incline, it picks up speed. If it is moving, it has kinetic energy.
But where did it come from? To gain energy, it must come from somewhere else. In the case
of the cart, it comes from gravitational potential energy. The mechanical energy is the sum of
PE and KE at any point in time.
Objectives:
-Identify what happens to the Potential and Kinetic Energy of a cart as it rolls down an incline.
-Determine how the Mechanical Energy changes as a cart rolls down an incline and what causes
this change.
Procedure:
1. Place 2 text books under the bottom of one end of the track and
leave the other end resting on the lab table. Determine the mass
of the cart being used in the lab.
2. Turn on the computer and start the Logger Pro program.
3. Place the motion detector to the end of the raised section of track.
4. Connect the LabPro or LabQuest Mini interface to the computer and motion detector.
5. Place the cart on the track so that the back of the cart is about 20cm from the motion detector
which is the minimum distance an object can get to detector and still get data. This will be the
zero position (x=0.0cm). Note what the track position is at this point (the tape measure on the
track). Measure the height of the track at this point (call it Point A), the height of the track
10.0cm down the ramp from A (call this Point B), and 20.0cm down the ramp from A (call this
point C), 30.0cm (point D), 40.0cm (Point E) and 50.0cm (Point F). Fill in the data table with
these heights in meters. (keep 3 sigfigs)
6. Zero the motion detector and then hit collect- once you hear the motion detector taking
measurements, release the cart and stop the cart towards the bottom of the track before it goes
off the track. You should have position and velocity information recorded on the screen.
7. Use the examine tool or the table of data to record the velocity when the cart is at 0m, 0.10m,
0.20, 0.30, 0.40 and 0.50m, or as close as you can get to these points (Points A, B, C, D, E and
F, respectively)
Data:
mass of cart:____
Point A
Height (m)
Velocity (m/s)
PE (J)
KE (J)
ME (J)
Point B
Point C
Point D
Point E
Point F
Analysis:
Transfer the data recorded in steps 5 and 7 in the a table. Using the values added to the table,
calculate the values for Gravitational Potential Energy and Kinetic Energy at Points A, B and C.
Also calculate the change that occurs in the Potential Energy and the Kinetic Energy.
Remember, the equation for Gravitational Potential Energy is mgh and the equation for Kinetic
Energy is ½ mv2. Use g = 9.81 m/s/s for your calculations. Show your calculations in your lab
notebook. Find the mechanical energy of the cart at each point. (Keep 3 sig figs for all answers)
Analysis Questions: Answer each question as completely as possible using complete
sentences. Show all work when answering.
1. How did the potential energy of the cart change as it moves down the ramp? How much
did the PE change from point A to F?
2. How did the kinetic energy of the cart change as it moves down the ramp? How much
did the KE change from point A to F?
3. How did the mechanical energy change as the cart moves down the ramp? Were these
changes significant as it moves from point to point?
4. Does gravity do work on the cart as it rolls down the incline? If so, how did we account
for this work?
5. Does the normal force do work on the cart? If so, how did we account for this work?
6. Does any other force do Work against the cart as the cart rolls down the incline? What
data from the lab supports your answer? Explain.
If a force did work against the cart as it rolled down the incline, what was that
force? How much work was done by this force on the cart?
7. Use the total distance of your cart’s displacement which you measured (Point A to Point
F) and the Work done by the force in #6 to find the size of this force.
8. Using your knowledge of equipment learned during the year, explain how could you
improve on the collection of data for the procedure to produce clearer results.