I did some even problems in the book that were not assigned in class. The book doesn't give me the answers to them, so if anybody could check out the problems and tell me if my solutions are correct that would be great.


1. The voltage, V, in a simple electrical circuit i slowly decreasing as the battery wears out. The resistance, R, is slowly increasing as the resistor heats up. Use Ohm's law, V = IR, to find how the current I is changing at the moment when R = 400, I = 0.08 A, dV/dt = -0.01 V/s and dR/dt = 0.03.

My answer: -0.010.

If the sound with frequency f*s is produced by a source traveling along a line with speed v*s and an observer is traveling with speed v*s along the same line from the opposite direction toward the source, then the frequency of sound heard by the obeserver is

f*o = ((c + v*o)/(c - v*s))f*s

where c is the speed of sound, about 332 m/s. Suppose that, at a particular moment, you are a in a train traveling at 34 m/s and accelerating at 1.2 m/s^s. A train is approaching you from the opposite direction on the other track at 40m/s, accelerating at 1.4m/s^2, and sounds its whistle, which has a frequency of 460 Hz. At that what is the percieved frequency that you hear and how fast is it changing?

My answer: 567.12 hz/s