2010 AP Physics B Discussion Thread

Test Preparation AP Test Preparation
101

<p>im taking this exam 2moro and i have no idea what half of you guys are even talking about!..yet why am i not panicking? o_O >.<</p>

<p>anyway, when a box is in a slope how do you find its normal force again??</p>

102

<p>^The normal force equals the weight of the box times the cosine of slope’s angle.</p>

103

<p>any last minute
“***? is that” facts</p>

104

<p>Yes, problems involving switches in a circuit and what closing/opening the switches does. I remember I had a bunch of those in a practice test and I got all of them wrong.</p>

105

<p>okay and also with circuits…how do you freaking know how to add up the resistors when they’re in ■■■■■■■■ combinations??
such as this:
<a href=“http://www.cheng.cam.ac.uk/research/groups/electrochem/JAVA/impedance/figure/sparal2.gif[/url]”>http://www.cheng.cam.ac.uk/research/groups/electrochem/JAVA/impedance/figure/sparal2.gif&lt;/a&gt;&lt;/p&gt;

106

<p>^dude thats hella easy.</p>

<p>just follow the resister rules. resisters in series just add. resisters in parallel are 1/R=1/R1+1/R2…etc.</p>

107

<p>R2 and R3 are in series, as are R4 and R5. Those can be “combined” into 1 resistor. From there, you should have 2 pairs in parallel. Use the 1/R=1/R+1/R…to get the total resistance of the 2 parallel pairs. Then, add the 2 numbers up, since they’re now in series.</p>

108

<p>are the PR tests easier than the actual AP?</p>

109

<p>Does anyone know what the curve for the PR is, it seems they didn’t provide one. And, my teacher claims that the curve is about 60% for this for a 5, but that seems a little low, any clarifications?</p>

<p>^ Actually, I think the PR tests are harder. I took a few released exams and other than the 1994 one (which was horrid), the rest were easier.</p>

110

<p>hmm 60% sounds rather low… are you sure? I didn’t think the PR tests were that hard, but Ive done only the first one yet.</p>

111

<p>My teacher said that you have to get a 50/70 on the multiple choice and do decent on the free response (never explained what decent meant, but did say that the key to a five is the multiple choice) in order to get a five.</p>

112

<p>Hey everyone. If you go on AIM thru meebo.com right now, and hit the Group Chat button to join a chatroom, you can join the chatroom named apphysb for intense AP Physics B prep. Have ALL your questions answered!</p>

113

<p>Someone please help me…
How do you answer #11 and #12 in the Physics B course description.</p>

<ol>
<li>What is the current in the 4 Ω resistor while the switch S is open?</li>
</ol>

114

<p>Yeah 60% did sound low, that’s why I was asking. No the PR tests aren’t that hard, I just thought they were harder than the actual AP. But the 2nd test is tricky at parts and has a mistake repeated in two questions (#45 and 46). </p>

<p>Here’s another practice question:</p>

<p>If a certain material with length L and area A has a resistance R, what must the resistance be of a piece of the same material with half the length and twice the area.</p>

<p>a. 1/8 R
b. 1/4 R
c. R
d. 4R
e. 8R </p>

<p>They always ask a resistance question, so this one should be easy by now.</p>

115

<p>i get stumped whenever they ask which units are the same like, what can be the units of gravitational force and then there are three totally different ones of different constants. i suck at those. any help?</p>

116

<p>i cant understand how to do the 2nd FRQ in the course description about the runner</p>

117

<p>Someone please help me…
How do you answer #11 and #12 in the Physics B course description.</p>

<ol>
<li>What is the current in the 4 Ω resistor while the switch S is open?</li>
</ol>

118

<p>Tito, is the answer B, 1/4R</p>

119

<p>see when the switch is open no current flows in that upper branch with the capacitor. the total resistance in the circuit can be calculated by taking the 3 in series, which comes out to be 20ohms. current=12/20=.6ohms. </p>

<h1>12 now when the capacitor is fully charged no current will flow through that branch again. so we apply the same steps and find the potential drop across the 10ohm resistor(which is the same as that across the capacitor, because they are in parallel combination).V=IR=10*.6=6V</h1>

<p>can anyone explain Q2. FRQ in the course description please?</p>

120

<p>Q2 FRQ in Course Description:
A. you need a stop watch, either masking tape or chalk, meterstick or tape measure, and a starter’s pistol.
B/C. I would use tape to mark out every 10 meters until I reach 100 m, then I would start the stopwatch and the starter’s pistol at the same time, and stop the the stopwatch when the runner reaches the finish line. Other classmates will use their stop watches, and stop each stopwatch every 10 meters. The portion where the times ends up to be the same is the portion with uniform acceleration. So now I have the total time, and the portion where the runner ran with uniform acceleration. Then use the big three to calculate the acceleration.</p>