It is highly unlikely that SAT II Physics will ask a question that involves remembering and then plugging numbers into an equation like this one. Remember: SAT II Physics places far less emphasis on math than your high school physics class. The test writers don’t want to test your ability to recall a formula or do some simple math. Rather, they want to determine whether you understand the formulas you’ve memorized. Here are some examples of the kinds of questions you might be asked regarding the pulley system in the free-body diagram above:
Which of the following five formulas represents the acceleration of the pulley system? You would then be given five different mathematical formulas, one of which is the correct formula. The test writers would not expect you to have memorized the correct formula, but they would expect you to be able to derive it.
Which of the following is a way of maximizing the system’s acceleration? You would then be given options like “maximize M and m and minimize
,” or “maximize
and m and minimize M.” With such a question, you don’t even need to know the correct formula, but you do need to understand how the pulley system works. The downward motion is due to the gravitational force on m and is opposed by the force of friction on M, so we would maximize the downward acceleration by maximizing m and minimizing M and
If the system does not move, which of the following must be true? You would then be given a number of formulas relating M, m, and
. The idea behind such a question is that the system does not move if the downward force on m is less than or equal to the force of friction on M, so
.
These examples are perhaps less demanding than a question that expects you to derive or recall a complex formula and then plug numbers into it, but they are still difficult questions. In fact, they are about as difficult as mechanics questions on SAT II Physics will get.
以上所介绍的就是SATII物理专题分析Pulleys，大家在复习的时候可以进行参考。