Physics for the Inquiring Mind [Phys 105]                Spring 2005
Exercises for St. Patty's Day, Thursday, March 17!

[1] Around the lab room, you will see six tracks set up.  Each group should go to one of these set-ups.

[2] To start, we will be measuring how long it takes your ball to roll a certain horizontal distance on your track.  Find the spot on your inclined track that is 15 cm above the lab bench.  Mark this spot, either with a pencil or with a piece of tape.  This is the point from which you will release your ball.

[3] Place your two photogates a distance of 20 cm apart on the horizontal section of the track.  Double click on the Shortcut to Lab109P2 icon on the desktop.  A display with 3 tables should come up.  Hit the START button (above Table 1) on your timing software.  Release your ball from the marked position on the track and let it roll down.  A time should appear in each of your three timing tables.  Do this three more times, and then push the STOP button on your timing software.  Record the mean travel time between the gates (this is the one listed in the Tgates table).

[4] Repeat the procedure in part [3] with the photogates spaced at distances of 30 cm, 40 cm, and 50 cm.

[5] Use the data that you have collected to complete the table of “Time” vs. “Distance Traveled” shown below.  I have included the entry (0,0) because we know that it takes no time to travel a distance of 0 cm.

Time (seconds)
Distance Traveled (cm)
0
0
20
30
40
50

[6] Use Excel to make a plot of “Time” vs. “Distance Traveled”, with “Time” displayed on the horizontal axis.  What does your plot look like?

[7] Is your ball moving at a constant speed when it is on the flat portion of the track?  How can you tell from your plot?  If you find that the ball is traveling at a constant speed, what is that speed (remember that speed is distance traveled divided by the time it took).

[8] Let's suppose that you want the ball to move at a speed of 120 cm/s when it is on the flat portion of the track.  Figure out how high above the track you need to release it in order to accomplish this.

[9] Homework due Tuesday, March 22: Do Exercise 6.3 on page 672 of McDermott.