Well! Two physics teachers wrote in with their results! I post both below, with their own words. Take a look at Nadia's to see how to use the Sparkvue app to get the kinetic energy data to display. See Joey's for a picture of his setup and how to adjust the D = 0 position.
First is Nadia Lara of St. Agnes Academy in Houston. Her writing is available at her blog, Need to Know Science. She says:
I set up the problem you wrote about last month and got the following graph with a 100 Hz sampling rate:
I used the spring attached to the smart car on the second setting. It’s pretty stiff, so the curve is steep and it’s harder to see the quadratic vs. linear relationships, but you can get plenty of data points. Higher sampling rates didn’t work well. A weaker spring would work better. I ended up taping a piece of a balloon on the bottom of the car to get enough friction to slow the car down quickly.
To get the calculated values, click on Experiment Tools on the bottom right, then choose “Calculated Data” -->
Type in your formulas. Use the orange “Measurements” button to select the measured quantities you want to insert into the equation.
To edit the units associated with a calculated value, place the cursor on the line of the quantity you want to update and click the Properties button. Click the keyboard button next to the units and type in the units you want.
Now Joey Konieczny of Atlanta's Drew Charter School:
I was [bored in a place where it's politically incorrect to admit to boredom], so I pulled up your blog and accepted your challenge. It took me a few trials to get it right, but below is my setup using the Smart Cart and two snapshots [overlaid on the same graph] from SparkVue showing Kinetic Energy vs. position. In Trial 5 I pressed record (this sets the zero position for the wheels) and pulled the Smart Cart back only the length of the piston. You can see from the graph that the Smart Cart thinks that zero position is actually about 15 cm ahead of where I told it zero was. Trial 7 I "cheated" and moved the cart forward 15 cm (pulling it back a total of 20 cm) and voila! The Kinetic Energy calculation (y-axis) was pretty easy, and Pasco has a ton of online resources to help figure it out.
I'm a huge fan of the Smart Carts. The data they spit out is awesome!
Thank you, Joey!