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. 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 = 1.6x10^-13 J; 235 g of U has 6x10²³ atoms.

a. How many atoms of ²³⁵U are there in 10⁹ metric tons of natural uranium?

b. What is the energy release possible from the ²³⁵U in 10⁹ metric tons of natural uranium?

c. If all the world's current power needs (7x10¹² W) were supplied by ²³⁵U fission, how long would this supply of uranium last?

3. The first atomic bomb released energy equivalent to 20 kilotons of TNT. If 1 ton of TNT releases 4x10⁹ J, how much uranium was consumed through fission in the bomb? Assume 208 MeV per fission; 1 MeV = 1.6x10^-13 J; 235 g of U has 6x10²³ atoms. Hint: use the energy released and the energy per unit mass of uranium.

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. Why?

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?