Question

In the challenging problem of 2.Problem Solving and estimation, I do not understand how it got derived from step 1.9 to step 1.10

Answer 1

Lets suppose the distance between Oklahoma and Lincoln = 800 km
Let's take the day that the sun could be directly over head in Oklahoma
In the same time the sun are going to be not directly on Lincoln = Angel of 7.2

The angle of the inclination of the sun's ray=7.2
The earth's circumference can be calculated as the following considering the value of 360:

Answer 2

You need to compare M_earth to M_europa and assume that the densities are approx. equal. This results in M_earth/M_europa=R_earth^3/R_europa^3. Put this into 1.9 and substitute F_earth=mg_earth and F_europa=mg_europa. The point mass "m" cancels out and you are left with Eq. 1.10.

Answer 3

thanx I didn't get the assumption part.... bah.. how did you know that we were supposed to assume density? nice one