Cracking the SAT Physics Subject Test

what’s being accelerated.

When doing your net force

calculations, bear in mind

that the system of objects

accelerates at the

same rate.

21. In the previous example, calculate the magnitude of the tension
    in the cord.

Here’s How to Crack It

Since the magnitude of a has been determined, we can use either of the two original
equations to calculate FT. Using equation (2), Mg − FT = Ma (because it’s simpler),

we find

FT = Mg − Ma = Mg − · g = Mg = (10)(10) = 25 N

As you can see, we would have found the same answer if we’d used equation (1):