# Homework 2.

1. Thought # 11, p. 56.

There must be a force acting on a body moving in a circular path: circling requires changing direction; changing direction means acceleration; acceleration means force.

2. Thought #12, p.56.

Because angular momentum is conserved (stays constant), the satellite speeds up as it moves closer to Earth. (Ang. mom. = (mass) x (radius to orbit center) x (velocity), so if radius goes decreases, velocity must increase to keep angular momentum unchanged.)

3. Problem #18, p.57; use table 2.2, p.49.

Take cube root of left column, and square the result; you should get middle column.

4. Review Question #3, p.80.

The graphics are too hard to do on this page -- sorry! Check this, though: if it's waxing, it's bright on the right; if it's waning, it's bright on the left. But as for the table, with approx. times (assuming sunrise at 6:00 a.m., sunset at 6:00 p.m.):
 phases new wx. cres. 1st qtr. wx. gibb. full wn. gibb. 3rd qtr. wn. cres. rises sunrise 9 am noon 3 pm sunset 9 pm midnight 3 am sets sunset 9 pm midnight 3 am sunrise 9 am noon 3 pm

5. Review Question #5, p.80.

Angle of illumination of sunlight, and length of day.

6. Thought Question #9, p.80.

a) equator; b) pole; c) equator; d) equator; e) within Antarctic Circle

7. Problem #20, p.81.

a) star rises four minutes earlier per night: (60 nights) x (4 min) = 240 min = 4 hours. So it's up at 4:30 p.m. -- even though you can't see it 'cause the Sun's up!

8. No state in the continental U.S. ever has the Sun in its zenith. Why? What state does have the Sun in its zenith sometimes?

a) The Sun only appears in your zenith (and then only on some days) if you're within 23.5o of the equator, and none of the continental us falls within this zone.
b) Hawaii is far enough south.

9. Problem #21, p.81.

a) (lat. of A.C.) - (lat. of T. of C.) = (90o - 16o) - 16o = 58o
b) seasons wouldn't vary as much