105 Physics Problem Set 4
Due: Thursday, October 15, 2009, 3 PM
Reading: K&K, Chapters 4 & 6. We are skipping chapter 5, but feel free to read it; it
contains some useful material.
Turn this in to the Undergraduate Physics Oce in Jadwin 208 by 3:00 PM on Thursday.
Please NEATLY write your name and the time of your class on your homework.
Our rst midterm exam is Mon., Oct. 19, in class. The problems on this exam will
be from the material in the rst 4 problem sets, and Chapters 1-4 of K&K.
Problem 1. Sports/power/work/food.
(a) A strong human cyclist, weighing about 110 kg (including bicycle), can bicycle up a
3.1 percent grade at about 30 km/h. What is her or his power output in watts? in
horsepower?
(b) How does this compare to a typical human oce worker climbing stairs in an oce
building at a rate of one oor every 20 s?
(c) How many kilocalories (which are known as calories in nutritional information) would
you have to eat every day to sustain each of these (relatively high) levels of activity
for 3 hours per day?
(d) A person an with active lifestyle eats 3 to 5 thousand kilocalories per day. Do you
think that the production of mechanical work is the primary use of food calories?
Note: to do this problem, you will have to look up some conversion factors, and you will
have to estimate the typical height per oor of an oce building. Many useful conversion
factors can be found in the front cover of K&K.
Problem 2. A particle of mass m experiences a force that depends only on the particles
position. The force is given by Fx = 6xy ; Fy = 3x2 3y 2 ; Fz = 0. Calculate the work done
by this force as the particle moves from the origin (0,0,0) to the point (x1 , y1 , 0) via these
two paths:
(a) (0, 0, 0) to (x1 , 0, 0) to (x1 , y1 , 0).
(b) (0, 0, 0) to (0, y1 , 0) to (x1 , y1 , 0).
Problem 3. K&K 4.12
Problem 4. K&K 4.13. Note: You will see similar problems when we cover central force
motion.
Problem 5. K&K 4.23. Initially, the balls are at rest as drawn, with the lower edge of
the superball at height h above the oor.
Problem 6. K&K 4.29
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