Answer:
The time take is 
Explanation:
From the question we are told that
The decay constant is
The percentage fall is 
The equation for radioactive decay is mathematically represented as

Where is
is the new amount of the new the isotope while
is the original
At initial
% = 1
At
% = 0.80

=> 
=> 
You get circular motion, where the acceleration is pointing towards the center of the circle, as long as they are constant, and not fluctuating.
Piper rockelle and I just got off the phone number
Answer:

Explanation:
By Snell's law we know at the left surface




now we have


now on the other surface we know that
angle of incidence = 

so again we have

so we have


also we know that


By solving above equation we have
