# University of California, San Diego Physics 11 - Survey of Physics

 H. E. Smith Fall 2004

 Physics 11 - Lab Exercise #1

## Velocity and Acceleration

In this lab exercise you will attempt to bomb a toy train from the balcony on the west side of WLH. Below is a drawing of the Laboratory Apparatus. Your bombs --- small sandbags --- will be provided

As shown, you will take up ambush where along the West balcony of the Warren Lecture Halls Building. You are to drop your bombs blind. (As in bombing in bad weather or at night.)

Because you know you are to bomb blind, your agents have placed Photogates A and B along the railroad track directly below the two plumblines at points A and B. Whenever the train passes through one of these gates you will hear a beep. Your agent has also laid measuring tape along the balcony between A and B, so you can measure whatever distances you may wish to know. The only other piece of equipment you will be issued is a stop watch. Again, it will be up to you to use it the way you see fit. (Hint: Chewing on it won't help.) Intelligence has given you the drop altitude h = 4.95m, and you are guaranteed that the unsuspecting train will keep a constant speed along the track between A and B, running parallel to the balcony.

### Homework (10 pts)

You are to hand in your homework to your TA at the beginning of the lab. Keep a duplicate for your own use. The homework consists of your detailed strategy for hitting the train and should include:
• Your written solution to nthe last problem on Homework #3 (The one about Prof. Smith & the egg) - use this as a guide for your lab strategy. Include your solution in your homework submitted.
• A brief description of the measurements that you will need to make.
• An estimate of the accuracy with which your measurements need to be made.
• A description of how you will determine when to drop your projectile.
Because you don't know the numerical values of certain parameters before actually taking up battle station along the balcony, you will have to assign them letter symbols in your battle plan. Extra credit will be given those plans whose equations keep to symbols to the last minute, even for known quantities such as g or h, before moving on to numerical answers. Only symbols, not numerical values frozen and conglomerated, allow you to predict what will happen should a certain quantity vary, e.g. what do I have to do differently should I have to bomb on the moon, where gravity is no longer the same?

### Lab Report (40 pts)

You will, of course, perform the experiment with your lab partners, and you may jointly calculate the results, but the report should be your work alone, in your own words. Lab reports that are overly similar will be penalized and may receive no credit. Reports are due in lecture 1 week following the date of the experiment. Your write-up of the lab should describe the reasoning behind your strategy, the procedures you employed and your "score" of hits. Demonstrate that your hits and misses are not random events. You must defend your campaign quantitatively. Among effects you might consider are:
• Air drag, air buoyancy
• Reaction time
• Velocity of the egg at release
• Size (length, height, width) and speed of target.
The completeness of your analysis will count more toward your Lab Score than your record of hits and misses.

The following rules apply:

1. Students enrolled in Physics 11 only please!
2. Each member of your team must drop an bomb from a different position along the balcony. Space yourself at least half a meter from your neighboring bombers so hits and misses can be assigned unequivocally.
3. For each drop post one member of your team downstairs, as observer to keep tab of hits versus misses, under TA supervision. Also to let you know if you have missed the train sideways, presumably because you have pushed the bomb a little too far over the ledge. It is a good idea to lay your bomb ready on the edge of the balcony, and to give it a slight push when it is time. Single shots only please.
4. The staging area for the train is separated from the walkway by plants. These plants are for everyone to enjoy. Anyone caught stepping on or over them, instead of using the access provided, will be penalized on his/her lab score.
5. Anyone caught leaning over the balcony, will be penalized in his/her lab grade.
6. Highest scorers with correct computations may be invited, in a grand finale contest at quarter';s end, to repeat the experiment with Prof. Gene Smith taking the place of the train. Drops only, no throws. (But remember who does the final grades.)
Have fun, good bombing.

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