** HL Physics Before / after **

decisions

6 iii a 1.128x10^-3 , b 7651.5 m/s
v 3.88x10^6, 5.4274x10^22

Did anyone else get those?!

ahmdoda

Leaving Cert Student wrote: »

q7 was tricky I thought? For drawing out the diagram of the sound waves, what did ye do?? I did the first 4 harmonics but then scribbled out the second!

yes it was! i wondered wether the 1st harmonic they gave was the 1st harmonic/fundemantal but their was no way of knowing as it could be divided it self by 2 to give lower harmonic i drew the graphs asuming it was the 1st. but the last part of the question when they asked for the tension how did u get the mass per unit length?! i stood their thinking about if for ages wondering weather to divided the mass given by the total length of 12m or the length taken of 64!

xJEx

decisions wrote: »

6 iii a 1.128x10^-3 , b 7651.5 m/s
v 3.88x10^6, 5.4274x10^22

Did anyone else get those?!

I only got the first two. but i think im wrong cause that sounds right based on the actual mass of the earth. how did you caculate the force??

Leaving Cert Student

decisions wrote: »

6 iii a 1.128x10^-3 , b 7651.5 m/s
v 3.88x10^6, 5.4274x10^22

Did anyone else get those?!

Think so

Jackobyte

Leaving Cert Student wrote: »

q7 was tricky I thought? For drawing out the diagram of the sound waves, what did ye do?? I did the first 4 harmonics but then scribbled out the second!

I drew this with frequencies 550, 1100, 1651 going from top to bottom:

xJEx wrote: »

I looked up the diagram in the book and the points are slightly off there too. To be honest, mine looked fairly similiar to the straight line in the book

I'm not saying I am right, I was just explaining my thought process. In the exam, I was thinking a thin conductor was similar to a filament in a bulb. I dunno the answer and am anxious about it. However, taking the slope between each point and the previous point, the slope decreases in steepness every time.

decisions

xJEx wrote: »

I only got the first two. but i think im wrong cause that sounds right based on the actual mass of the earth. how did you caculate the force??

I used the period to calculate the mass of the earth and then used that to get the force of attraction. I'm not sure how to get the force of attraction without the mass of the earth.

Anyone have answers for the Q8 calculations?

Leaving Cert Student

ahmdoda wrote: »

yes it was! i wondered wether the 1st harmonic they gave was the 1st harmonic/fundemantal but their was no way of knowing as it could be divided it self by 2 to give lower harmonic i drew the graphs asuming it was the 1st. but the last part of the question when they asked for the tension how did u get the mass per unit length?! i stood their thinking about if for ages wondering weather to divided the mass given by the total length of 12m or the length taken of 64!

yeah I messed up the diagrams coz I realized then when I had to calculate the speed of sound from them than the 2nd and 3rd wouldnt work. I changed them around to suit that then and I got speed of sound to be 330ms in all three. Did anyone use a formula other than c=f[lambda]... I was getting paranoid trying to use the 4(l+0.3d) formula

xJEx

decisions wrote: »

I used the period to calculate the mass of the earth and then used that to get the force of attraction. I'm not sure how to get the force of attraction without the mass of the earth.

Anyone have answers for the Q8 calculations?

Yeah that was my problem.. I tried to get the centripetal acceleration and then used F=ma

Jackobyte

decisions wrote: »

6 iii a 1.128x10^-3 , b 7651.5 m/s
v 3.88x10^6, 5.4274x10^22

Did anyone else get those?!

Pretty much the same. My mass of the earth came out as 5.95x10^22, but I had carried all nine decimal places of ω up to that point which may have accounted for the difference.

ahmdoda

Leaving Cert Student wrote: »

yeah I messed up the diagrams coz I realized then when I had to calculate the speed of sound from them than the 2nd and 3rd wouldnt work. I changed them around to suit that then and I got speed of sound to be 330ms in all three. Did anyone use a formula other than c=f[lambda]... I was getting paranoid trying to use the 4(l+0.3d) formula

i dont think their is another forumula to use but yea it should workout to be 330

Jackobyte

decisions wrote: »

I used the period to calculate the mass of the earth and then used that to get the force of attraction. I'm not sure how to get the force of attraction without the mass of the earth.

I used F=mrw^2 with m being the mass of the ISS.

Leaving Cert Student

decisions wrote: »

I used the period to calculate the mass of the earth and then used that to get the force of attraction. I'm not sure how to get the force of attraction without the mass of the earth.

Anyone have answers for the Q8 calculations?

It was centripetal force formula to get the force of attraction.

then equate this answer with newtons universal gravitation formula to get mass of earth.


and lastly period of ISS sattelite had to equal period of this new sattelite as they were geostationary. I got something like 10000000 seconds

decisions

Jackobyte wrote: »

I used F=mrw^2 with m being the mass of the ISS.

I totally forgot about that formula! What I did was correct anyway, just not the way they wanted me to do it.

The last part of that q was 24hrs for a geostationary orbit? I didn't put it into seconds properly

Jackobyte

Leaving Cert Student wrote: »

yeah I messed up the diagrams coz I realized then when I had to calculate the speed of sound from them than the 2nd and 3rd wouldnt work. I changed them around to suit that then and I got speed of sound to be 330ms in all three. Did anyone use a formula other than c=f[lambda]... I was getting paranoid trying to use the 4(l+0.3d) formula

That other formula was only for closed pipes AFAIK. You were grand not using it.

Leaving Cert Student wrote: »

and lastly period of ISS sattelite had to equal period of this new sattelite as they were geostationary. I got something like 10000000 seconds

I said the period had to be the same as the earth rotation for it to remain above the same location at all times, i.e. 24hours which came out to 86400 seconds or so.

no scope codgod

xJEx wrote: »

I looked up the diagram in the book and the points are slightly off there too. To be honest, mine looked fairly similiar to the straight line in the book

It wouldn't have been a straight line the whole way. The book specifies that it is only within this limit that it is directly proportional. As you increase the Current there will be a heating effect, causing the resistance to rise as well. This explains why the graph started to curve slightly toward the higher values for the voltage.

Eurovisionmad

Why did the astronauts "appear" to be weightless?

Leaving Cert Student

Jackobyte wrote: »

That other formula was only for closed pipes AFAIK. You were grand not using it.

I said the period had to be the same as the earth rotation for it to remain above the same location at all times, i.e. 24hours which came out to 86400 seconds or so.

but I thought it had to be the same as the ISS orbit as this is what it was geostationary with? damn i think i was wrong

decisions

Eurovisionmad wrote: »

Why did the astronauts "appear" to be weightless?

The ISS is in a constant state of free fall towards the earth.

In 10 why was the tube evacuated?

Leaving Cert Student

Eurovisionmad wrote: »

Why did the astronauts "appear" to be weightless?

State of freefall due to gravity?

Orladee

ItsCon wrote: »

Does anybody know if they're putting the values back on the paper or if we'll have to use log book again? There was a lot of problems last year with people taking values at different decimal places which gave a wide range of correct answers

Ahh they did that again this year. very annoying!

decisions

5 (e) 1.239x10^8 ??? The speed of light in a diamond.

Leaving Cert Student

Damn I ****ed up q6... for q5... last bit what was the answers for (J) minimum frequency of photon

OR

event occurring in LED

Undeadfred

decisions wrote: »

The ISS is in a constant state of free fall towards the earth.

In 10 why was the tube evacuated?

So it was a vacuum so the particles wouldn't collide with air particles

decisions

Leaving Cert Student wrote: »

Damn I ****ed up q6... for q5... last bit what was the answers for (J) minimum frequency of photon

OR

event occurring in LED

F=2mc^2/h?

ahmdoda

Undeadfred wrote: »

So it was a vacuum so the particles wouldn't collide with air particles

that what i said! but my then people said because alpha praticles had a short range in air

Eurovisionmad

decisions wrote: »

The ISS is in a constant state of free fall towards the earth.

In 10 why was the tube evacuated?

Damn that is good! I said centrifugal force but I knew it had to be wrong cause that's not even on the course in any big way!

Leaving Cert Student

decisions wrote: »

F=2mc^2/h?

I had that but thought the answer would need to contain unknowns as it was an expression so I changed it to something which in hindsight was stupid jesus what an annoying question.

if I answer both options for J will they take my best one?

Glee_GG

Leaving Cert Student wrote: »

It was centripetal force formula to get the force of attraction.

then equate this answer with newtons universal gravitation formula to get mass of earth.


and lastly period of ISS sattelite had to equal period of this new sattelite as they were geostationary. I got something like 10000000 seconds

For geostationary I didn't do any calculation? In our book it had a bit where it said that if an object was geostationary its period is 24 hours, same as the earth so I just wrote that down?!

Orladee

Leaving Cert Student wrote: »

q5 was tough ya what was the principle of storage heater??

Is it not the Specific Latent Heat? takes it in at night cheaply and lets it out slowly, or is that even a principle?

Jackobyte

Leaving Cert Student wrote: »

Damn I ****ed up q6... for q5... last bit what was the answers for (J) minimum frequency of photon

decisions wrote: »

F=2mc^2/h?

Yeah, E=2mc^2. I went a step further and filled in the mass of the electron though to solve for a specific value. Wasn't sure whether they wanted that done or not.

EDIT: Crap, never went and found the corresponding frequency from E=hf. Did extra questions in that section anyway so hopefully I still have 8 right ones.