# Science Tutors

 Subject Science Due By (Pacific Time) 12/14/2016 04:00 am

Could you answer 3 questions below? (in 6hrs)

If you find yourself stuck on these remember these "hints" to help you get started:

For the 1st: speed=distance/time -> so time = distance/speed

For the 2nd and 3rd: The half life is discussed in the slides. Remember the definition of a half life- after one half life you have half of your original sample back. So after two half lives you have (1/2)*(1/2)=(1/4) of your sample left. After 3 half lives you have (1/2)*(1/2)*(1/2) of your sample left. In general, after n half lives your fraction of your original sample is (1/2)^n.

I hope this helps.

1) Assume you wanted to have a discussion with a civilization located near the center of the Milky Way Galaxy.  What would be the minimum time between sending the signal and receiving a reply? Hint. we live about 2.5x10^20 meters from the center of the galaxy.

2) Assume you have a sample of atoms with a half-life of 0.25 second.  Approximately how much (in %) of the original sample will be around after 1 second?

3) Potassium-40 decays to Argon-40 with a half-life of 1.25 billion years old. If at the formation of the Earth we had 100% Potassium-40 and 0% Argon-40, what should be ratio of Argon-40 /  Potassium-40   on the Earth today?

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