Physics 105 - How Things Work - Fall, 1998

Problem Set 2

• Due Monday, October 26, 1998, in class
• If you need to turn in any assignment early (or late), put it in the padlocked box outside physics room 133.
• Please answer each problem as thoroughly and precisely as possible. You should think of this as a chance to show off your knowledge of physics. Each problem is in effect saying "Here is an interesting physics problem. Explain it thoroughly to the reader." For example, in Case 7 part d, don't just say "the readings increase" or "the readings decrease." Rather, explain the limits of how the readings change and what the horse can do to achieve those limits.
• The more concise and exact you are with your answers, the more credit you'll receive. This does not mean you should be verbose! To the contrary, you should think carefully before you begin to write.
• You may discuss the problems with one another but you must write them up separately and in your own words.
• Write your name and ID# clearly and legibly on the top of each page that you turn in, and staple them together. If you do not, you may not receive full credit.
• If your name and ID# are written so clearly that they can be read easily by a bleary-eyed student who hasn't slept for two days, you will receive 5 bonus points.

• Case 7, p. 119, all parts. For parts d and e, explain the limits of how the scale readings change. (For example, what if the horse "shifts its weight?")
• Case 9, p. 155-156, all parts.
• Case 6, p. 207, all parts.
• Review question 12, p. 204 (not to be confused with the exercise on the subsequent page). To answer this, you will need to explain what the "speed of sound in air" means.
• Consider a jar of pasta sauce, which contains the sauce itself and an air gap above the sauce. The contents are hot before the flexible metal cap is put in place. Explain (a) why the cap is indented (bowed downward) when you buy it (b) one way that you could make the cap bow upward without touching it or opening the jar (c) the sound you hear when you open a correctly indented new jar.
• How would a Frisbee fly on the moon? In other words, you give some spin and initial horizontal velocity to a Frisbee on Earth, and observe its flight. Then you repeat the experiment on the moon. What are the differences, and why?
• A 747 is flying to the west coast. A bumblebee is hovering inside. Does the airplane feel the weight of the bumblebee? Why or why not? In other words, imagine that the airplane with passengers is exactly at its weight limit, so that the addition of a stationary bumblebee on the floor of the aircraft would cause the plane to crash. You want to think about whether or not the addition of a hovering bumblebee inside the plane would cause it to crash. It may help to think of the bumblebee as a small helicopter.