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Church, Galileo, Uranium, Fission, Nearsighted and farsighted

1. In 1610, the Church started its attack on Galileo. They stated:

i) Suppose a cannon be fired, first due east, then due west. In one case the shot has the velocity of the earth as well as that of the force of the powder, in the other case only the difference of the two. But, in fact, no such difference is noted, and therefore the earth does not move.

ii) If the earth rotates as fast as Copernicus says, birds could not keep up with it!

Briefly, use physics to answer these two charges.

2. Please see the attachment.
3. Please see the attachment.

4. You were stranded on a desert island with John, who wears glasses. He manages to start a fire. Is John nearsighted or farsighted? Explain how you know. Explain what nearsighted and farsighted mean, and how glasses correct the condition.

5. Give brief answers to following questions.

a. Why is the sky blue?
b. Why are clouds white?
c. Why is the sunset red?
d. If you are looking at a rainbow, where is the sun and why?

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1. In 1610 the Church started its attack on Galileo. They stated: i) Suppose a cannon be fired, first due east, then due west. In one case the shot has the velocity of the earth as well as that of the force of the powder, in the other case only the difference of the two. But, in fact, no such difference is noted, and therefore the earth does not move. ii) If the earth rotates as fast as Copernicus says, birds could not keep up with it! ... Briefly, use physics to answer these two charges.

Solution: i) If the speed of the cannon fired due east and fired due west is measured by an observer stationed away from the earth's surface and stationary relative to earth's centre, the observer will indeed measure different speeds. As the earth is rotating from west towards east, to the observer the cannon's speed will be as follows:

When fired due east: VC = VCE + VE ..........(1) where VC = Velocity of cannon relative to the observer, VE = Velocity of earth relative to the observer, VCE = Velocity of cannon relative to earth

When fired due west: VC = - VCE + VE ..............(2) (-ve sign added to VCE as the due west is opposite to due east)

However, when the observer is positioned on earth and is stationary relative to it, what is being measured is the velocity of the cannon relative to earth i.e. VCE. As we can see from (1) and (2) magnitude of VCE is same in the two cases viz. VE - VC . Hence, the cannon's speed measured by an observer on earth for both the directions is same.

ii) Birds fly relative to the atmosphere (air) surrounding the earth and the atmosphere rotates alongwith the earth being bound to it by the force of gravity. Hence, the speed of a bird relative to the air is same as that relative to earth. In other words, with the atmosphere rotating with earth and the birds flying relative to the atmosphere, the birds have no problem in keeping up with the rotation of earth.

2. It has been estimated that the Earth contains 109 metric tons of natural uranium that can be mined economically. Of this total, 0.7% is 235U that can be fissioned to produce energy. Assume 208 MeV per fission; 1 MeV = ...

Solution Summary

Church, Galileo, Uranium, Fission, Nearsighted and farsighted is examined.

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