Investigation 10B: Work and energy
Essential questions: How is the work done on a system related to its change in energy?
How is the efficiency of a system calculated?
Have you ever pulled a swing back and let it go? The work you do to pull the swing backward and
upward is converted into gravitational potential energy. When you let it go, gravitational force does
work on the swing pulling it downward and speeding it up, transforming its gravitational potential
energy into kinetic energy. Gravity does work on the swing; as a result, the swing’s kinetic energy
changes. In this investigation you will explore the relationship between work and kinetic energy by
measuring the work done on a cart to accelerate it, and then comparing that work to the cart’s change
in kinetic energy.
Part 1: Constant Force
1. Set up the equipment like the picture below.
2. Open the experiment file 10B_WorkEnergyTheorem, and then connect the Smart Cart using
Bluetooth.
3. Unhook the thread from the cart and measure the mass of the cart plus the two 250-g cart masses.
Record the mass value above the table on the next page.
4. In your software, zero the Smart Cart force sensor while nothing is touching the hook.
5. Reattach the thread, and then roll the cart all the way to the end of the track opposite the pulley and
hold it in place.
6. Start recording data, and then release the cart to roll freely down the track. Catch the cart before it
rolls into the pulley. Data recording stops automatically after 1.5 seconds.
7. Use the tools in your software to determine the net work Wnet done on the cart (Wnet = area under
your force versus position data), and the measured final speed of the cart. Record the work and
speed values in the Part 1 row in the table on the next page.
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