Deaf Hunters and Hostile Aliens(Bring quad ruled comp books tomorrow for your PJ)

Here is an eclectic mix of problems to get you thinking. Enjoy!

1. You are being chased through the forest by a deaf hunter named Elmer who is convinced that you are the prize-winning buck he has been looking for. He has you pinned down behind a log 450 m away but Elmer only has one bullet left in his .30-06. You are wondering if you can stick your face up over the log to draw his fire and still have time to duck when you see the flash of his gun. Elmer’s gun shoots bullets with a speed of 820 m/s. You figure it will take you 0.45 s to duck after you see the flash. Can you risk sticking your head up? (It is always a good idea to sketch physics problems, so sketch this one.)

HW #1

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2. Hostile aliens vaporize the Sun. (The Sun is normally about 8 light minutes away.)

A) Where is the Sun’s light 4 minutes after the Sun is vaporized*? Sketch the light from the Sun (use yellow ink!) in cross-section. Note the Sun’s original location.

B) Do earthlings know anything has happened to the Sun 4 minutes after vaporization? How long after vaporization will it take before earthlings know that the Sun is gone?

C) Speculate about what will happen to the Earth as time goes by.

*Assume that “vaporized” means instantly removed from our universe.

AliensNot to Scale!

Sun’s former location

EARTH

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Take a rough guess before you do any math and record your guess here:

Now do the math, using estimates and approximations. Explain each step!

*A light year is the distance light travels in a year. Light travels 186,000 mi/s or 3.0 x 108 m/s.

Scale Milky Way Diameter Guess =

Scale Milky Way Diameter Calculation = =

(alg) (#)

3. Now let’s change gears and try to get a handle on the scale of the Milky Way Galaxy we live in. Our sun is one of about two hundred billion stars in a disc that is 100,000 light years* across. Reduce the Sun (1 million miles across) to the size of the period at the end of this sentence. How far across will our scale galaxy be?

2MASS map of half a billion stars in our Milky Way Galaxy

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