AP Physics B Post Exam Discussion [LOL FRQ]

<p>@skorpius i did the same thing as you. no idea if it’s correct. that equation just happened to incorporate all the variables.</p>

<p>paranoia…</p>

<p>Skorpius, I did the same thing, but I was totally guessing.</p>

<p>Squiggly, I put that no it didn’t, what did you put?</p>

<p>@squiggly</p>

<p>no the formula for single slit maxima is dy/L = (m+1/2)lambda</p>

<p>i said yes it did. if i calculated correctly the moving electron had 4.something eV of kinetic energy and 2eV was required for the atom to be excited to n = 2</p>

<p>I put that you couldn’t know since you didn’t know the atom’s mass and therefore couldn’t use E=pc to find the energy since you didnt have the atom’s momentum post-collision</p>

<p>Wait, the ground state is n=1, right?</p>

<p>i said yes, but it was a complete guess. and my justification was total bs, i found the wavelength with momentum then did some crazy things with planck’s constant…
was the photon in the visible spectrum? other choices were radio and xrays</p>

<p>i put visible</p>

<p>@garfield</p>

<p>yes</p>

<p>@squiggly</p>

<p>i put down x-ray but it was either x-ray or visible.</p>

<p>Did everyone else think #1 was obnoxiously easy?</p>

<p>and this is kind of a stupid question from the first frq, but how do you find the acceleration at t=3? i used calculus for the entire question, so i just found the rate of change using v(5) and v(0)</p>

<p>@zach</p>

<p>yes, but it was a false prophet</p>

<p>@squiggly</p>

<p>the object’s acceleration was constant from t=0 to t=5 so you’re good.</p>

<p>I said not enough info lol since Idk if the collision is perfectly elastic or not.</p>

<p>Well, the energy is 3 eV, which is 4.8E-19 J. Divide by h and divide c by the answer, and you get 400 something nanometers, which is visible.</p>

<p>Squiggly, since acceleration was constant wouldn’t it have just been 2?</p>

<p>Acc is the slope of the velocity…</p>

<p>@Skorpius</p>

<p>Here’s how I started out for number 5:</p>

<p>Constant velocity so no net force thus Fe=W
Fe=E<em>q and E=V/d therefore Fe=V</em>q/d=m*g</p>

<p>I can’t remember, but they wanted us to solve for q right? so q = m<em>g</em>L/V</p>

<p>That’s stupid. Since when is knowing which wavelengths of light are part of the visible spectrum something we have to know?</p>

<p>Okay, so I think I got almost everything on all questions except 3, which I failed on since I didn’t use(or know) the single slit formula</p>