Homework 4 - Physics 150 Fall 2003
Due MONDAY September 29, 2003
Write a short paragraph describing the meaning of conservation laws and why they
are so important in science. Argue whether you believe they tell us something
about nature or instead tell us about the human mind's ability to invent quantities
so that their sum is conserved.
In class there was a demonstration of a drop of dye put into clear
water. Describe what happens when the dye is dropped into the water.
Explain how this relates to the second law, the tendency toward more probable
states, and increase in disorder.
Write in your own words short essay answers to the discussion questions II-11
on p. 276 of Lightman. Grades will be given based on the scientific content of
your answers, NOT on whether or not you agree with Morris' arguments.
- March, Chapter 5, exercise 8.
- Two people standing at rest on ice (assumed to be frictionless) push each other
apart. The larger person has mass 90 Kg and moves at a speed of 1.5 m/s.
Find the speed of the smaller person if he/she has mass 40 Kg.
- A roller coaster of mass 800 Kg starts with zero velocity at a height of 35 m.
It goes through many turns and a loop, finally coming to rest at a height of 17 m.
How much energy was lost to heat?
- A baseball of mass 0.25 Kg moving at 50m/s is caught in a glove. Assuming
all the energy goes into the glove, much heat energy is added to the glove?
If the glove has mass 0.3 Kg and has the same heat capacity as water, how much
would the temperature of the glove increase?
- A heating element on a stove converts 1000 Watts of electrical power to heat.
How many calories of heat are generated in one minute? How long would it take
to bring to the boiling point 5 Liter of water starting from room
temperature of 20 C?
- This problem is similar to the example on p 52-53 of Lightman, but with more
realistic numbers. Suppose there is 0.02 Kg of oxygen gas at temperature 30 C
in the cylinder. The cylinder supports a mess of 5Kg at a height of 0.3 m.
Heat is added to the gas, increasing its temperature to 330 C, and raising the mass
to a height of 0.6 m. Calculate the work done on the mass in Joules and in calories..
Calculate the total heat input in calories.
- An important technological goal is to make heat engines that operate at
higher temperatures, for example the turbines in power generator plants. Give the
fundamental physics reasons why one must operate at higher temperature for greater
efficiency. What is the maximum possible efficiency of a steam turbine in which the
steam enters at 1000C and exits at 100C.
EXTRA: Explain why the numbers given in the example on p 52-53
of Lightman are not realistic for that example as shown in the figure.
(This is "extra credit" in the sense that it will be noted
along with class participation and other factors in the discretionary part
of the grade.)
Remember that there are hints, examples, and worked exercises,
In March there are answers
to odd-numbered problems that are very similar to problems assigned.