<p>I’m guessing 23 is E because it says it’s suspended in the air?
No idea for 24.</p>
<p>^ Hahah I just made that example up, but seriously, we should do it.
I saw you say you’d eat your shoe!</p>
<p>@TheMysteriousOne: Found them, great.</p>
<p>Abrayo that question with angular momentum as answer is a biiiiiiitch of a question.
well for one, kinetic energy is not conserved because Ki does not equal Kf because chemical energy from the body comes into play.
next, linear momentum is not conserved because the axle of the wheel applies a force to the wheel in response to the force with which the boy jumped off. This force however acts tangentially to the axis and therefore doesn’t cause a torque so no change in angular momentum is created by the axis. But the external force by the axle makes the linear momentum not be conserved.</p>
<p>^ ohman.
So in general is it true that something leaving a rotating disk would not be a conservation of angular/linear momentum? Or does it only apply in that situation? If so, why?</p>
<p>CAN ANYONE PLZ TEELL ME IF the Princeton review tests are harder??? Cause they are harder than 1998, 1993 released tests.</p>
<p>yes, linear momentum will NOT be conserved but angular momentum WILL
this is true for anything that spins on an axle and has something jumping on/off of it.</p>
<p>PR just has different questions not necessarily easier or harder</p>
<p>Wait, why isn’t linear momentum conserved? Because one thing will continue to spin and the thing jumping off won’t?</p>
<p>So if i get like 30 correct on the released tests and 22 correct on the princeton. What should i expect tomorrow?</p>
<p>Probably around a 30 since that’s what you got on the real thing . . .</p>
<p>@salzahrah:
What about this one?</p>
<ol>
<li>A long board is free to slide on a sheet of frictionless ice. As shown in the top view above, a skater skates to the board and hops onto one end, causing the board to slide and rotate. In this situation, which of the following occurs?
(A) Linear momentum is converted to angular momentum.
(B) Kinetic energy is converted to angular momentum.
(C) Rotational kinetic energy is conserved.
(D) Translational kinetic energy is conserved.
(E) Linear momentum and angular momentum are both conserved.<br></li>
</ol>
<p>It says the answer is E. (this is from 2004)
I don’t have the image though. I thought it probably would have been A?</p>
<p>as mentioned before, the axle provides an external force on the system. Linear momentum is only conserved if the net external force = O. The net external force is not 0 in this case and therefore linear momentum is not conserved.</p>
<p>you should expect a 5 if u score at least 9’s on all of your FR.</p>
<p>Omg, what if the FRQ’s are HELL this year???</p>
<p>To make up for the no-guessing penalty?
I hope not. They’re already bad enough as it is.</p>
<p>Chemistry and Calculus were both harder than usual… If physics is harder, I’ll go ballistic.</p>
<p>Oh well. Is a 4 a good score for Mechanics?</p>
<p>Linear momentum is conserved if there is no net external force, angular momentum is conserved if there is nonet external torque. If a force is applied along a line directed radially towards or away from an axis of rotation, angular momentum is conserved because that does not produce a torque. If you are talking about linear momentum, work is only done along the line of motion, so if you have a force that is perpendicular to the path, it does no work. That is why the magnetic field can actually be considered a conservative field although the magnetic force is not a central force.</p>
<p>With the skater and the long board, since both objects are included in the system, you have no external forces or torques. The internal forces between the two object (for instance the force of the skater stepping on the platform perhaps multiple times) do not need to be specified because in this situation Newton’s third law applies.</p>
<p>Yeah, I’ve heard that AP Physics C Mechanics is the hardest out of all the physics tests.</p>
<p>if there is planets with semielliptical orbits i will shoot myself</p>
<p>^untrue E/M is a *****</p>
<p>Thank you both for the momentum explanations! I understand it now.</p>
<p>How would you approach a semielliptical orbit problem?!
Would they ask you to draw orbits? I know that was already on a past one though.</p>
<p>the more i think about it, the more i realize how fked i am for this exam(s).</p>
<p>^ You’re kidding.
If you looked at my practice FRQ . . . oh man.
Going to bed soon. I hate Physics!</p>
<p>ugh i keep screwing up the first part of the problem, which then leads to like a 5/15.</p>
<p>Yeah!
Sometimes I just have no idea how to approach a problem.
I REALLY REALLY hope there isn’t a torque problem.
How do you apply a torque to a bar attached to a wall, when the bar is held up by a string?
Does the torque equal the tension in the string or . . . ?</p>
<p>Also:
An object is thrown with velocity v from the edge of a cliff above level ground. Neglect air resistance. In order for the object to travel a maximum horizontal distance from the cliff before hitting the ground, the throw should be at an angle θ with respect to the horizontal of
(A) greater than 60° above the horizontal
(B) greater than 45° but less than 60° above the horizontal
(C) greater than zero but less than 45° above the horizontal
(D) zero
(E) greater than zero but less than 45° below the horizontal</p>
<p>Why is it C? I was looking for ONLY at 45°. If only 45° was an option, would it be correct? Doesn’t a projectile at 45° travel farthest?</p>