Galactic Dynamic Homework (Problem 2.1 of B&T)

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TL;DR Summary: Why the topic give the condition "limρr^5/2=0“?What is the usefulness of this condition? Thanks!

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You are trying to prevent infinities from popping up in the PE. This is more strict than trying to prevent infinities from popping up in the mass.
 
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TL;DR Summary: I came across this question from a Sri Lankan A-level textbook. Question - An ice cube with a length of 10 cm is immersed in water at 0 °C. An observer observes the ice cube from the water, and it seems to be 7.75 cm long. If the refractive index of water is 4/3, find the height of the ice cube immersed in the water. I could not understand how the apparent height of the ice cube in the water depends on the height of the ice cube immersed in the water. Does anyone have an...

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