Cracking the SAT Physics Subject Test

as simply as possible.

6. If M is the mass of Earth, then the mass of the Moon is about
   M/80 and the mass of the Sun is about 330,000M. If R is the
   distance between Earth and the Moon, then the distance between
   Earth and the Sun is about 400R. So, which exerts a greater
   gravitational force on the earth: the Moon or the Sun?

Here’s How to Crack It

According to Newton’s law of gravitation, the gravitational forces on Earth exerted
by the Moon and by the Sun are:

and

Simplifying these expressions, we compare the values of

Compare, Don’t

Complicate

Comparison problems

are very common on the

SAT Physics Subject Test,

so remember that they

don’t always have to be

completely solved. For

instance, in this example,

the two forces share the