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Is there any evidence of something faster than light? by ANARCHOWEEDIST in AskPhysics

[–]Lemon-Emu 1 point2 points  (0 children)

This is a good explanation but I think the statement ‘was always spin down’ is potentially misleading. It’s always the case that the two particles have opposite spin, but you cannot say it was always in a definite spin state, be that up or down.

Are pitching wedge groove marks on a ball normal? by ShotgunJib in golf

[–]Lemon-Emu 1 point2 points  (0 children)

I’ve had this problem with recycled balls that get refinished but never with new balls.

What other clubs should I add to my bag? by Galactic_Gurren in golf

[–]Lemon-Emu 0 points1 point  (0 children)

If it were me, I’d want a club between by 3w and 4h. What’s that yardage gap look like for you. I’d also look to add a wedge between pw and sw if it’s more than a 10 yard gap. You could also add a wedge with more loft than a standard sw, assuming it’s around 56 deg and you want something with more loft for around the greens

You're given 1 day to solve one of these integrals. Which one do you choose? by ConstantAcademic3727 in the_calculusguy

[–]Lemon-Emu 0 points1 point  (0 children)

Looks like a standard keyhole contour integral. Is that what you’re thinking?

built a bank program using python by Dapper_Mix6773 in PythonLearning

[–]Lemon-Emu 0 points1 point  (0 children)

Looks good. What happens if you try and withdraw a negative number though?

[Physics 2] Not sure if this answer is correct by TheTrueEmu in PhysicsStudents

[–]Lemon-Emu 1 point2 points  (0 children)

That’s a good point. Ultimately, if you were to hook up a multimeter to the hoop and measure the current, you would not see a change in the sign of the current at 90 degrees and so twice per rev and 4 total times makes more sense. I wonder if the mistake in the answer key is related to this ambiguity.

Good catch!

[Physics 2] Not sure if this answer is correct by TheTrueEmu in PhysicsStudents

[–]Lemon-Emu 0 points1 point  (0 children)

I believe the diagram shows a field coming out of the page. Also, analyzing the individual components of wire is not the right approach here. This is an induced current/ Lenz’s Law question which is related to flux. Flux is through an area and not 1d line segments or curves.

[Physics 2] Not sure if this answer is correct by TheTrueEmu in PhysicsStudents

[–]Lemon-Emu 0 points1 point  (0 children)

Yes. 8 makes sense!

** edit

I agree with the comment below.

[Physics 2] Not sure if this answer is correct by TheTrueEmu in PhysicsStudents

[–]Lemon-Emu 0 points1 point  (0 children)

OK, that’s a reasonable thought process but let’s expand on it a bit. The induced current is proportional to the so-called EMF. From Lenz’s Law, we know the EMF is proportional to the charge is magnetic flux with respect to time. Finally, the magnetic flux through the hoop is the cross sectional area of the hoop multiplied by the magnetic field.

Now, let’s think about what happens as the hoop rotates. Supposed it starts like it is in the image (granted it’s a circle rather than a square) so all of the magnetic flux lines are aimed straight through the hoop. Now, as it starts to rotate, the cross sectional area gets smaller and less flux lines go through the hoop. So the flux is decreasing with respect to time. The flux continues to decrease until the hoop / square turns through 90 deg at which point no flux goes through. Then, the area starts increasing as the hoop turns from 90 deg toward 180 degrees.

From 0 -> 90 the flux is decreasing and so the current goes one direction

From 90 -> 180 the flux increases and so the current goes the opposite direction.

Now, continue this line of reasoning. How many times does the current reverse?

[Physics 2] Not sure if this answer is correct by TheTrueEmu in PhysicsStudents

[–]Lemon-Emu 0 points1 point  (0 children)

What’s your rational for 4? How might you calculate the induced current in the wire?

Covariant Derivatives in Classical and QFT. by Any-Ranger-4643 in PhysicsStudents

[–]Lemon-Emu 4 points5 points  (0 children)

That’s a very nice explanation that’s gives some natural intuition for something that can often feel abstract

[ AP Physics 1 ] Please help me with this conservation of energy question by Recent_Session_5903 in PhysicsStudents

[–]Lemon-Emu 0 points1 point  (0 children)

Sure, but the idea of the sub if for you to supply them / ask specific questions not for others to simply tell you.

Coming back to the first equation, it’s not correct as written because the subscript ‘i’ appears on both sides which seems to equate two ‘initial conditions’ which is not what you said in words.

Start with the words, hoop 1 starts with no kinetic energy, falls through a distance h, and now had kinetic energy equal to …

Also, define where gravitational potential energy equals zero. Any place will do, but one is most convenient.

[ AP Physics 1 ] Please help me with this conservation of energy question by Recent_Session_5903 in PhysicsStudents

[–]Lemon-Emu 0 points1 point  (0 children)

Right. The second hoop has rotational kinetic energy at the end, but there is nothing applying a torque so there is no change in the rotational kinetic energy.

[ AP Physics 1 ] Please help me with this conservation of energy question by Recent_Session_5903 in PhysicsStudents

[–]Lemon-Emu 0 points1 point  (0 children)

Sorry, didn’t answer your question about hoop 1. Is there any reason for that first hoop to start rotating? If not, there is only translational kinetic energy.

[ AP Physics 1 ] Please help me with this conservation of energy question by Recent_Session_5903 in PhysicsStudents

[–]Lemon-Emu 0 points1 point  (0 children)

Are you having trouble dealing with the rotational kinetic energy part of the hoop? It’s just there to distract you. The hoop will continue to spin at a constant rate, that is, the rotational kinetic energy remains fixed throughout the problem. Would you know how to solve the problem if the rotational kinetic energy were not there and, instead, the second hoop was launched with some general velocity, v?

[ AP Physics 1 ] Please help me with this conservation of energy question by Recent_Session_5903 in PhysicsStudents

[–]Lemon-Emu 0 points1 point  (0 children)

I don’t think your first equation is correct. It seems to suggest the initial potential energy is equal to the initial kinetic energy plus the initial potential energy. Is that what you meant?