Lab 3: Two-Dimensional Momentum, Estimation, and Dimensional Analysis



Two-Dimensional Momentum Conservation

Consider the multiflash photograph of a collision of two billiard balls. Assume that the time interval between flashes is .1 second. Do the measurements below reasonably carefully.

  1. Choose a coordinate system. (A clever choice will make the problem a little easier.)
  2. Determine the velocity vectors for each of the balls before and after the collision. Write the vector as both a magnitude and direction in component form.
  3. Determine the momentum of the system before and after the collision. Write your answer as both a magnitude and direction and in component form.
  4. Is momentum conserved?


Dimensional Analysis

From P. Tipler, Physics for Scientists and Engineers, Third edition, Worth Publishers, 1991.
  1. The period T of a simple pendulum depends on the length L of the pendulum and the strength of earth's gravitational field g. Find a simple combination of L and g that has the dimensions of time.
  2. Check the dependence of the period T on the length L by measuring the period for three different values ofL. (The period T is defined as the time for a complete to-and-fro swing.)
  3. The correct formula involves a numerical factor that is dimensionless and hence can't be obtained by dimensional analysis. Using your data from the above question, estimate the value of the numerical factor.


Estimation: Potatoes

  1. You are visiting a local organic potato farm and are discussing the possibility of buying the farmer's potatoes to use in the COA dining hall. The farmer is very interested and asks you approximately how many pounds of potatoes COA would need each month. Come up with an order of magnitude estimate of the pounds of potatoes used in the dining hall each month. Do this problem without a calculator.
  2. How many acres of land would be needed to grow these potatoes? Consult the seed catalog. Apparently in Maine soil it is possible to get around 20 lbs of potatoes from one pound of seed.
  3. How much would the seed cost? What is the approximate value of the crop?
  4. How many acres of land would be needed to feed the entire population of the United States for one year? Assume that we all eat nothing but potatoes.
  5. How many acres would be needed to feed the world potatoes?


[Dave] [Physics I] [COA]

Web page maintained by dave@hornacek.coa.edu.