How Long Until Superman Regains His Powers?

AI Thread Summary
Superman is affected by kryptonite that decays exponentially, and he will regain his powers once 90% of it has disintegrated. The decay constant is given as r = -0.138629. The calculations involve setting up the equation Q(t) = Qe^(rt) and solving for t when 90% of the kryptonite has decayed. The attempt at a solution resulted in t being approximately 16.6 days, indicating that Superman will regain his powers after about 17 days. Accurate calculations are crucial for determining the exact time frame for Superman's recovery.
Yohan Lee
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Homework Statement


superman has been disabled by a nearby amount of kryptonite, which decays exponentially. If Superman cannot regain his power until 90% og the kryptonite disintegrates, then how long will it be before he regain his powers?
Use r=-0.138629. Round to the nearest day.
a. 4days c 11days
b 6days d 17days e 21days

Homework Equations


Q(t) = Qe^(rt)

The Attempt at a Solution


i tried 0.9Q=Qe^(-0.138629t)
0.9=e^(-0.138629t)
ln0.9=lne^(-0.138629t)
ln0.9=-0.138629t
ln0.9/-0.138629 =t
t=0.760018
and i was not able to find the answer
 
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If 90% has decayed, how much is left?
 
Thank you i got 0.1Q=Qe^(-0.138629t)
t= 16.6
 

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