Video Lab: Blowdart Colliding with Cart Printer Friendly Version
This lab is based on a Direct Measurement Video called Blowdart Colliding with Cart released on the Science Education Research Center (SERC) website. The copyright for this video belongs to Independent School District 197 in Mendota Heights MN. The project is partially funded by a National Science Foundation Grant (#1245268) awarded in September 2013.

The following lab directions were designed for use in my Honors Physics I class and only represent one method of analyzing the data provided in the video.

Using data from the video we will calculate the momentum of a blowdart and cart both before and after a collision. Then we will discuss conservation of momentum and any changes in KE that occurred during the collision. Before taking any measurements, view the video several times to acquaint yourself with its scenario.

Refer to the following information for the next four questions.

This initial section of questions deals with the dart's average speed prior to colliding with the cart.

 On which frame does the tip of the dart just start to emerge from the pneumatic gun?

 On what frame does the tip of the dart reach the 45-cm mark on the video's scale

 How much time in seconds does the dart take to reach the cart?

 What was the dart's average speed before impacting the Styrofoam on the cart?

Refer to the following information for the next two questions.

According to the background information given with the video, the mass of the dart is 28.3 ± 0.1 grams and the mass of the cart is 250.3 ± 0.1 grams. Now we will investigate the magnitudes of the dart's momentum and KE before its collision with the cart.

 Calculate the total momentum in the dart/cart system before the collision.

 Calculate the total KE of the dart before the collision.

Refer to the following information for the next three questions.

Our next section deals with calculating the average speed of the dart/cart system as well as the final momentum and KE of the system after the collision.

Between frame +0 and frame +19, the center of mass of the embedded dart and cart system moves forward 5 cm.

 What was the average speed of dart/cart system after the collision?

 What was the total momentum of the dart/cart system after the collision?

 What was the total KE of the dart/cart system after the collision?

Refer to the following information for the next six questions.

Conclusions
Do your answers for the total momentum before the collision and the total momentum after the collision verify that momentum was conserved during the collision?
 Support your choice in the previous question.

 What is the percent difference between the total momentum before the collision and the total momentum after the collision?

 What percent of the dart's original KE was lost during this collision?

 Is this collision elastic or inelastic?

 What impulse does the cart give to the dart in this collision?