Hi my teacher set this but i dont think there is answer to part (a)?

So I had an exam the other day and the following fusion equation was given:
4H -> He + 2 positron
*H is made up of 1 proton and no neutron
The mass defect of the Helium is given as 0.0030337u and positron has no binding energy
In the calculation for energy released by fusion, do I need to take into account the mass of positron or is the energy released the mass defect only?

(I included the positron in my calculation but my teacher didn’t (He said it was because positron has no binding energy))

So I had an exam the other day and the following fusion equation was given:
4H -> He + 2 positron
*H is made up of 1 proton and no neutron
The mass defect of the Helium is given as 0.0030337u and positron has no binding energy
In the calculation for energy released by fusion, do I need to take into account the mass of positron or is the energy released the mass defect only?

(I included the positron in my calculation but my teacher didn’t (He said it was because positron has no binding energy))

A construction worker takes a 55-kg board of length 6.0 m and places it so that 2.0 m are extending out beyond the edge of a building. The worker has a mass of 40-kg. How far out beyond the edge of the building can the worker walk before the board begins to rotate? Assume that the edge of the building is the pivot point.

I came to the conclusion that the board would start to rotate at 2.51 m, so he could walk all the way to the end of the board.

55/3 = 18.33

(4m)(36.67kg) = x(40kg + 18.33kg)

x = 2.51 m

The answer key does the following:

r(40kg) = (1m)(55kg)

r = 1.4m

where does the 1 meter come from, and isn't the weight of the board divided between each side of the pivot point (55/3*2 and 55/3)?

Thank you to anyone who helps!

B asks to find the minimal angle that would not break the cable. to answer this i combined both masses of the beam and the sign, and found the new centre of mass. i used this to calculate the minimal angle. when i looked online for similar answers, and consulting AI, they assumed the sign's centre of mass is at 0.75m; the same as the beam. the sign is flush with the end, with a centre of mass of 1.0m relative to the beam.
am i missing something, or are the text books wrong in this case

I know that a1 = -a2/2 is physically correct and I’ve solved the question already but my initial attempt yielded a1 = -a2 and I couldn’t figure out what went wrong. Please help

Hey everyone. I was trying to use the suggested parity argument to work out the second current. So, it is clear that these different constants like m, E_1, M, and E_2 are kinda superfluous and don't really affect the problem, so we can use this parity property to work out the solution and substitute the correct constants afterwards.

This was my method:
Replace the adjoint up spinor(p4) with adjoint down spinor(p3)γ⁰ and down spinor(p2) with γ⁰ up spinor(p1).
Next, I realized that the gamma sandwich is just γ^μ adjoint, so it simply keeps the 1st component of the current the same, while flipping the others.
Then, I went back and replaced the constants with the current constants for the muons.

This method worked to solve line 1, but when I applied the same logic to line 2, I get an extra minus sign in front.

I checked that up and down helicity states transform the same way under parity, and that adjoints transform as I stated earlier. In addition, they both pick up a phase factor of -1 under parity, which seems to cancel when you introduce it into the current equation.

Anyone got any idea? Thank you so much in advance, this question is driving me up the wall. Would greatly appreciate any help.

The problem says:

A source of light emits a photon in a direction perpendicular to the direction of relative movement of this source with respect to an observer in the lab. Determine the frequency seen in the laboratory in relation to the frequency in the source reference frame.

Now first of all, I know wording's shit so I assumed it's perpendicular in the source frame for both approaches. I know it could mean perpendicular in the lab frame, but doing it that way with both approaches also led to different results so here we go:

Also for both, lab frame is S and source frame is S'.

Approach 1: four-momentum:

Doing a Lorentz boost to the four momentum you get:

E'=hf', E = γhf', hf = γhf', f= γf'.

Approach 2: events and Lorentz transforms:

Both crests of the photon appear at the same location in S' with a time difference between them of 1/f', so the time between both emisions in S is γ(1/f') then 1/f = γ/f' and you arrive at f= f'/γ.

I believe approach 2 is incorrect but I don't know why

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 reasoning.

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 = 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. If the provided answer isn't wrong, please help me understand where I went wrong in my chain of thought.

i've already solved this problem but i was curious about what a diagram for this problem would look like? would the circuit have a switch? would everything be in the shape of a rectangle? is the power source within the rectangle to show series or outside the LC rectangle? it would be great if someone could show me exactly how it would look like, thanks!

I’m lost here I need to find Ra and Rb

hey everyone, need a bit of help right now. this homework is overdue and i managed to finish the front page fine, but i have zero clue what to do for the back here and on the next page. would greatly appreciate full solve with explanation if possible!! (ik me asking for answers is not ideal for learning the material, but this hw situation is a bit desperate at the moment 😭)

I tried to solve for acceleration but it came out to be g(9.8m/s2), which means I am not making the FBD's correctly. Kindly guide me thanks.

The figure below shows two transverse waves traveling on strings. The linear density of each string is 0.065 kg/m. The tension is provided by a 26-N block that is hanging from the string. Find the speed of the wave in part (a) and in part (b) of the drawing (Cutnell and Johnson, 2012, p.497).

Here is the problem and the solution. I don't understand the highlighted parts.

If friction is suddenly turned on, irregularities should appear suddenly on its surface and friction should immediately come into play. Then why is the frictional force still zero?

in the next part, why would a stick be different from a rope? And what is the physical meaning of a negative tension?

Thank you

I find electricity extremely difficult and unintuitive. Where to start??

problem reads: determine the magnitude of the current in the eight ohm and two ohm resistors in the drawing.