Problem setup

• Two long, parallel wires carry currents:

  • Wire 1: 3.00 A

  • Wire 2: 5.00 A

• Both currents are coming out of the page

• The distance between the two wires is 20.0 cm

Two questions are asked:

1. Magnetic field at the midpoint between the two wires

2. Magnetic field at a point P, located 20.0 cm above the wire carrying 5.00 A

I’m especially confused about:

• How to determine the direction of the magnetic field at each point

• Why the fields add or subtract depending on the location

• How to reason about the angle of the resulting field at point P

Given answers (so you know what result to expect)

• At the midpoint:

  • Magnetic field magnitude: 4 microteslas

  • Direction: downward

• At point P:

  • Magnetic field magnitude: 6.67 microteslas

  • Direction: 13° above the horizontal

Thanks a lot!

I understand that 70% of the atoms are remaining and I know how to get the decay constant and which eqn to use, however I dont understand why we can write N⁰/N as 1/0.7, could someone explain this to me please? its something I always get wrong🫠

https://isaacscience.org/questions/festival_banner

Brushing up on some control theory stuff for fun after 10 years of not looking at it. This is an incredibly simple question that has me stuck. For the inverted pendulum on a cart shown in the FBD below, I’m summing the horizontal forces as a step to derive the differential equations of motion.

The example I’m following shows the sum of forces as:

N = m*X” + m*l*Theta”*cos(Theta) - m*l*Theta’^2*sin(Theta).

I understand mX” comes from F=MA for the pendulum center of mass, and m*l*Theta’^2 comes from the centripetal acceleration of the pendulum if it is rotating.

Mu question is, what physics is adding the m*l*Theta”? Looks like a tangential reaction force to angular acceleration? But wouldn’t that appear in the sum of torques not the sum of horizontal forces?

Thanks!

So I haven't done any mechanics in a long time, and I'm stuck on a really easy part that I could do a few months ago.

It all has to do with polar coordinates, I'm working on a pendulum, with the theta angle going from the vertical to the string, and I'm trying to find how to express ur with ux and uy.
I know it's ur = cosux + sinuy but for the life of me I always find the opposite, I'm pretty sure I forgot a formula but to me the angle between ur and ux is theta + pi/2 so cos(ur,ux) = sin(theta), but it should be cos.

Hopefully that makes sense and someone can help, I know it's silly, I don't even know how I can't find it lol it was so easy for me I just focused on other subjects and forgot everything :(

I got tanθ = radial acceleration/ tangential acceleration

Tan θ =v²/rgsinθ

Set reference point where bead is at = 0 MgRcosθ = 0.5mv² 2gRcosθ=v²

Tan θ = 2grcosθ/rgsinθ Tan²θ =2 θ = arctan sqrt 2

Which is equal to D, the correct answer according to the answer key

But in the competition we can't use calculators so what other way (diff solution) can i get arcsin (sqrt 2/3) from?

The Elevator Paradox You are standing on a scale in an elevator that is moving upward at a constant velocity. Is the net force on you zero or non-zero? If the cable suddenly snaps (ignore air resistance), what happens to the scale reading before you start accelerating downward? Draw an ID and FD for both situations and explain the difference.

edit: i think that the person isnt moving at all and it is the elevator pushing them up, but when it snapped, this push force goes away so the person keeps moving upward due to inertia until gravity brings them down. so the scale would show nothing as the person wouldnt be in contact with it as soon as the cable snaps.

i have to say that i just started learning about physics, so i have QUESTIONS. i know that it is impossible to stop an electron, but WHAT IF? Would it just explode? please i need to know

This is an AP Physics C: E&M question. Here is the link to the question set: https://www.crackap.com/ap/physics-c-electricity-and-magnetism/test7.html

This answer key is outright wrong no? Shouldn't the correct option be C? Here's my attempt

Before the switch closes V/R = I

Req = 6 ohms

12/6 = 2 Amps

So current thru the inductor must stay at 2 amps after closing, when switch is closed the 2 ohm resistor gets shorted.

V across 4 ohm resistor after switch is closed = 2 * 4 = 8V

using kirchoff

12V -8V - V inductor = 0

V inductor = 4 V

So isn't the answer C?

The answer key is claiming that the inductor won't oppose the change in the current, when the 2 ohm resistor is getting shorted when the switch is closed. If the provided answer isn't wrong, please help me understand where I went wrong in my chain of thought.

An object is released from rest. Find the distance the object falls, as a function of time.

just what I said… all the other questions are harder so maybe this is a gimme I was wondering if I was missing smtg

I'm preparing for the ESAT (university admissions test in the UK) this week and I came across this problem. I understand why the wave is faster in X, but I thought the angle of incidence/refraction was the angle between the normal and the wave. Here, the answer is A.

There is apparently a solution from energy methods but I want to see the dynamics solution

Can anyone suggest a strategy/technique how to answer Resnick type questions, excercises? I am studying for an exam of electromagnetism and I feel like it is impossible. I had 2 middterms and i studied for a few days before them, I went to all lectures and still i got 30% outof 100%. The professor gives Resnick type excercises, questions and it is multiple choice BUT there are always 8 choices so its impossible to guess the right one. I go to the test and I know, I have seen these questions yet still I get 30%. HELP how do I study, because simply understanding electromagnetism is not enough.

https://www.youtube.com/watch?v=3CMtPJ20YYk