<p>C) In an perfectly inelastic collision, the maximum amount of KE is lost and is converted into energy that causes damage or creates heat, so KE is never conserved. A and B are wrong since it would deny the principle of conservation of linear momentum and the key phrase is “free of external forces.”</p>
<p>My question:</p>
<p>If the electric field does negative work on a negative charge as the charge undergoes a displacement from Position A to Position B within an electric field, then the electrical potential energy </p>
<p>A) is negative
B) is positive
C) increases
D) decreases
E) cannot be determined from the information given</p>
<p>Actually, I thought that the total length of the board was 7 m. Moreover, i didn’t learn about center of mass (but the name itself is self-explanatory).</p>
<p>I’m going to state the answer when Keasbey Nights answers.</p>
<p>For Jerry’s question, V = EPE/q, and then dV = -W/q (I know that this is algebra based, so we’ll have dV represent delta V). Negative work would make the numerator positive, while a negative charge would make the denominator (and the final value) negative. The answer is D - voltage decreases.</p>
<p>I’m kinda taking a past MC test, and my score on it seems to be about 30… Do you guys think it’s possible I can pull that up to a 50 these two weeks?</p>
<p>Whoopsies! I feel silly. If you’ll notice, I answered in terms of voltage. I read “electric potential” and missed the “energy” at the end. Indeed, because dEPE = -W and work is negative, the change in EPE is positive, meaning that EPE increases and the answer is C.</p>
<p>A straight wire of length 2 m carries a 10-amp current. How much stronger is the magnetic field at a distance of 2 cm from the wire than it is at 4 cm from the wire?</p>
<p>Indeed, it is A. Good job to both of you. Here’s an open response problem from Cutnell/Johnson.</p>
<p>The security alarm on a parked car goes off and produces a frequency of 960 Hz. The speed of sound is 343 m/s. As you drive toward this parked car, pass it, and drive away, you observe the frequency to change by 95 Hz. At what speed are you driving?</p>
<p>The answer is about 17 m/s. Here’s why. Frequency changes by 95 Hz as you drive toward and pass the parked car. Doppler effect equation is: f’ = f[(v + vo)/v] for when a moving listener is getting closer the source. Because frequency changes 95 Hz overall, we can assume that frequency changes by 95/2 Hz when we’re approaching the car. Therefore:</p>
<p>960 + 47.5 = 960[(343 + vo)/343], and vo = 17 m/s</p>
<p>Guys, I need a lot of help on this test, and I would love to practice the MC on the newer released exams, however I don’t even know where to find them or even know if anyone has them. Any help? Also, I lack a main resource (money).</p>
<p>Pigeons (2 kg total) are roosting in a large, 20 kg closed-in coop. The whole thing is on a scale. Suddenly, a loud noise causes all the pigeons to fly, but they remain inside the coop. The scale reads:</p>
<p>A) 190 N
B) 200 N
C) 210 N
D) 220 N
E) Not enough info. Depends on whether birds are hovering, or accelerating up.</p>
<p>The answer is D, 220 N. As the pigeons fly upward, the force they exert on the air - in perfect physics world - will push just as much on the coop, registering 220 N (22 kg * g).</p>
<p>However, in perfect physics world, one wouldn’t even consider the air molecules in that problem, and the answer would be B. I don’t think this is prone to show up on the exam.</p>
<p>A police car catches a speeder and turns on its sirens. Once the sirens are turned on, both the police car and the speeder are driving at 30 m/s. When stationary, the siren emits a frequency of 900 Hz. The speed of sound is 343 m/s. What is the frequency that the speeder hears?</p>