General Physics I, Fall '10

Homework 7

Covers UP Chapters 5 and/or 6

As advertised, this will be a slightly unusual homework assignment. There are two problems below; you should do at least one of them. The first is basically a projectile motion problem. (I'd recommend doing this if you feel like you want or need to spend a little more time with the chapter 5 material -- but be warned it's rather challenging compared to the projectile motion problems we did last week.) The second is a friction force and F=ma kind of problem. I'd recommend doing this if you feel ready to move on to the kind of new material we covered in class Wednesday. You may do both problems for a bit of extra credit if you're so inclined.

1. In class last week we developed a formula for the range R of a projectile launched at angle a with initial speed v on level ground: R = (2 v2 / g) * sin(a) * cos(a). (See also the "ballistic zucchini" touchstone example on pages 115-6.) The goal here is to develop a similar formula which applies to non-level ground. So consider a hillside making an angle b with respect to the horizontal. A cannon launches a ball with initial speed v and initial angle a (also with respect to the horizontal, and note a > b) up the slope. Where does it land? (Check your answer by showing that it reproduces the "level ground" formula when b=0.)

2. In the classic 80's movie "teen wolf", Michael J. Fox's character (Scott Howard) "surfs" on the top of a van while driving around the city. See here:

(The spanish dubbed version was the first thing I found, and, well, it just makes it even funnier.)

Suppose the static friction coefficient between Scott and the top of the van is 0.8. If the van driver steps on the gas and accelerates from 0 to 60 miles/hour in 4.0 seconds, will Scott be able to stay on the roof? How about if the van goes around a curve -- a quarter circle of radius 70.0 meters -- at 60 miles/hour?

Last modified: Monday, December 19, 2011, 9:18 AM