HINT OF THE WEEK



CHAPTER 8


Numerical:


#1] Figure out the volume of each proton and neurton.  How
	many of them are there?  The total volume of all those guys added together will be  
	the volume of the Uranium Nucleus.  Use the formula to relate volume to radius.

#3] Use 5.00832x10^-27 kg for the mass of Helium 3

#4]  You have to figure out how many Joules of energy is the same as a million $ worth of energy.
	You then use the results of problem #3 which tells you how many joules you get for a
	given amount of mass (i.e. the initial mass).  Now figure out how many kilograms of 
	initial stuff (Deuterium, H two) you would need to get the larger amount of energy
	you calculated originally.	

#5] Similar to #4. Here you need to figure out how joules of energy the sun emits in one billion
	years.  You also have to figure out how many joules you get for each reaction (4H->He).
	How many kilograms of Hydrogen did the sun use in one reaction?
	How many would it need to use for the huge amount of energy it emits in one billion yerars?
		The answer is 2x10^28 kg, not 4.4x10^26 kg.

Discussion:

#1]What particles feel these forces?  Repulsive, Attractive?  Where do each interact?
	When does one dominate over the other?  

#3]Find out by Operating a Tokomak yourself.

#5] How long will they last?  What happens when a star burns up all its hydrogen?
	(I don't expect you to know the answer to this last question--however that 
	 shouldn't stop you from speculating. It never stops me, especially in section)
	




CHAPTER 7



Numerical:

#1] Time dilation---The pi-meson lives a certain amount of time as counted by her
	watch--us scientists in the lab say that the time is longer (dilated) measured
	by our watches.--- How much is this time dilated? Use the factor ala the
	example problem on pg. 210

#3] Pg. 213

#4] To free the electron you need to smack it with enough energy to break its bond  with
	the atom.  i.e. you need to knock with at least as much as the binding energy.
 	Pg. 223

#5] He gave the energy of the light emitted not the wavelength.--
	The wavelength is 8.2x10^-7 m   this is infrared light.
	You should be able to figure out how to get the wavelength 
	since you know the energy of the light.




Discussion:
#1] Think about this in terms of a time interval.  In one case the time interval
	is positive, the other it is negative.  Look at the equation for time dilation
	and see if this is possible.

#2] What do you do to something when you heat it up?  What does this change?

#4] Pg 216

#5] To do damage the light must be able to penetrate the outer layer of skin.
	Why would U.V. penetrate and not visible?  
	When light hits something and is absorbed it acts like a particle,
	meaning that light is absorbed one photon at a time.
	Why does this matter?

	





CHAPTER 5



Numerical:

#3] pg. 164

#5 & #6] Remeber from Thursday's lecture, that there is a transformer between the power plant 
	and the town.  

	Since energy is conserved => the rate of energy produced = the rate of energy consumed.  
	Meaning that the power on one side of the transformer = the power on the other side of the 
	transformer. 

 	Since you know the power and the voltage on both sides of the transformer--
	this means that if you know the current the town uses, 
	then you can calculate the current that the power plant must deliver to the transformer.   

	After figuring out the current flowing through the wire from the power plant you can use your 
	knowledge of the wire's resistance to calculate the power consumed by this wire.

	If you are still having trouble draw a picture and go slowly.

	There is actually something not quite right about problem #5] but if you don't care--
	you don't need to worry about it.  You should still get the answer given.
	If you do care then ask me about it.



Discussion:
#4] takes some thought, but give it a shot anyway.








CHAPTER 4





Numerical:

#2]  The height doesn't change so no potential energy in this problem.
	The block starts of f with kinetic energy, but this is converted to
	heat by the force of friction acting over 20m.
	

#5] This one is a doosey:
	Here is the main point--Hydroelectric power works by tapping into 
	the potential energy of water at some height.
	
	In the problem he gives you the amount of water falling a given height
	every second.  You must convert this into an amount of mass so you can
	calculate the potential energy available each second.

		The Density of Water is 1000 kg/m^3

	You also might need to convert from Joules to kiloWatt-Hours
	Remember that a  kiloWatt-hour = 1kW x 1Hr
	and 1 W = 1 J/s

#6] The answer to part b) is $0.027.







CHAPTER 3:





Numerical:

#4]  don't be fooled:  Diameter=100m ->  radius=50m  
			1 g = 1 x accel of gravity = 9.8 m/s^2 

	The answer given is the period of revolution (time for each revolution)

	Try finding the rate (rev/sec) this is the number of times around per second.
		If I'm standing on the edge of the donut--how many times will I
		go around in one second.	How fast am I going?  What distance
		do I go in one revolution. 	
	 	The answer is 0.07 rev/s  or  0.07 /s .     

	You probably already have a feel for rate of revolution but not in (rev/sec)
	Instead you've probably heard of something expressed in (rev/min), which
	is the number of revolutions per minute or rpm's.  Remember records players?
	Mine usually spins around 33 1/3  times every minute.







Discussion:

#1,2,4, are all discussed in the chapter.

#5]  Look at page 38 in Chapter 2

#3]  Figure out which one has the shorter period of orbit.  i.e. which one goes around the 
 	Earth quicker.






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