<p>Here's a review thread for the upcoming SAT subject test in Physics. I'll start:</p>
<p>Assume that every projectile fired by the toy cannon shown above experiences a constant net force F along the entire length of the barrel. If a projectile of mass m leaves the barrel with a speed of v, at what speed will a projectile of mass 2m leave the barrel?</p>
<p>(Please remember to show your work for all problems involving calculations)</p>
<p>lol is no one on CC taking Physics?</p>
<p>I am, I just didn’t see this.</p>
<p>OK, I’m assuming [the problem is worded kind of strangely; it seems like there should be an image we’re not seeing] that the projectile is subjected to force F in order to leave the barrel. Since the length of the barrel is unchanging, and so is the net force F, we can assume that the energy…imparted to the projectile is constant as well (W = fdcos(angle)).</p>
<p>So the energy for the first projectile = energy for the second; 0.5mv^2 = (0.5)2mv2^2. So in order for v2^2 to compensate for the 2m, it will half to be twice the first v^2. So v2 = v/(sqrt(2))?</p>
<p>^That’s how I interpreted it as well.</p>
<p>You folks know your right hand rules for magnetism? :)</p>
<p>^uhh isn’t it conservation of momentum?
p=mv, so m doubles, v= v/2</p>
<p>I remember seeing this problem before but I don’t remember how I did it.</p>
<p>the main point is that the constant force was acted upon the projectile while it was fired from the gun barrel.
F x d = change in kinetic energy
F x d = .5mv^2
now kinetic energy should be the same
.5mv^2 = .5 x 2m x (?) ^2</p>
<p>This is a conservation of energy, F x d, problem and not a conservation of momentum problem. So yes, the answer is v/sqrt2.</p>
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<p>But conservation of momentum involves interacting objects, does it not? This is just a cannon firing one object, then firing another. They aren’t bouncing off one another/there’s no recoil being considered/etc. so I don’t see how momentum is involved.</p>
<p>I remember seeing this question from the PR review guide.
Yes it is not about momentum but work = change in kinetic energy.</p>
<p>i took this in may, and it was so much harder than ap physics B</p>
<p>ended up with a decent 700 though :]</p>
<p>wait—its HARDER than AP PHYSICS!!!</p>
<p>i’m onhly in honors</p>
<p>ive been taking kaplan tests and they didnt seem that bad—is kaplan way too easy?</p>
<p>ahhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh…but hon physics at my school is SO hard</p>
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<p>I’m also curious about this quote. Could you specify why you thought it was harder? Comparing the AP and subject test material it would seem that the subject test is easier; there’s at least no fluid mechanics.</p>
<p>There are stupid questions like this:</p>
<ol>
<li> Which of the following uses the principle of electromagnetic induction?</li>
</ol>
<p>(A) Resistor<br>
(B) Electric generator<br>
(C) Electric motor<br>
(D) Capacitor<br>
(E) Voltmeter </p>
<p>Both the electric generator and electric motor uses electromagnetic induction, although the “best answer” would be generator.</p>
<p>lol B right?</p>
<p>princeton review SUCKS…the questions are NOTHING like what you see on the actual test…=/ bad experiences last time with it
try kaplan or sparknotes</p>
<p>Actually that question was from sparknotes…</p>
<p>well ok but you wouldn’t see a question like that on the real test though…i meant that sparknotes covers concepts better…its review questions are off too</p>
<p>i took the sat physics in may and during the test i was like ***FF none of these questions require math!!!
like a question had to do with light dampening or something</p>
<p>The answer to the initial question was v/sqrt(2).</p>
<p>Is this test easier/harder than Physics B AP test?</p>
<p>It’s definitely easier, but the curve is also much harsher.</p>