The slope of this graph is . Therefore, μ 0 must be the slope of the graph divided by the current inthe solenoid.
Similarly, imagine a graph of force vs. time on a question that asks for impulse. Since impulse is
equal to force times time interval (Δp = F Δt ), then impulse must be the area under the graph.
Finally, if you’re totally clueless about what to do with a graph, just try taking a slope or an area,
and see what happens! You might experience a revelation.Other diagram questions might ask you to:
• use the right-hand rule to determine the direction of a magnetic force on a particle
• identify the direction of an electric or magnetic field
• analyze the properties of a circuit
• recognize the correct free-body diagram of an object
• interpret motion graphs
Many other diagram questions are possible. Try making one yourself—pick your favorite diagram
from your textbook, and ask a question about it. Chances are, you have just written an AP multiple-choice
question.
Direct Solution with Variables
Because the AP test writers can’t ask you to do any kind of difficult number crunching on the multiple-
choice section, often they will ask you to do your problem-solving using variables only.
A pendulum of length L is drawn back to position P , as shown in the above diagram, and released from
rest. The linear distance from P to the lowest point in the pendulum’s swing is d ; the vertical distance
from P to the lowest point in the swing is h . What is the maximum speed of this pendulum in terms of
the above variables and fundamental constants?(A)