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# PHY4 Jun 05 Thread :( watch

1. I worked out the distance between all the nodes divided by 4 to find the average distance then multiplied that by 2 to find the wavelength. then used v = fλ can't remember my answer though.
did anyone else use that method?
2. (Original post by Economist)
Wavelength = 2 x node to node = 2 x 2.4 = 4.8
4.8 x 0.25 = 1.2
9.2 /1.2 = 8.17Hz
dis agree - foronthe logic , i understood that wavelength is distance from peak to peak - and so got 2.4x0.25,

but then again, i was confused so could well be wrong

off to revise for geog now - bye!
3. Node-Node = half wavelength since its a stationary wave

1) changing direction therefore change in accel so must have resultant force from f=ma.
w= 7.3 x10^-5 rad per sec
f=2.03 N
f =586.6N

2) visible light = 5 x10^-7
gamma = radiactive material eg uranium
micro wave = microwave oven

3) I = 76.4 x10^-3 W per m(sq)
photon = 2.0ev

4) amplitude = max distance from center of oscilations
2 cm
2.5 cm
1.6 cm

starting at 2 then going up then down etc

5)
motion of a hand perpendicular to direction of wave, i put transverese waves can be polarised too

differences: progressive is one wave,standing is a product of 2
progressive has wave shape, standing wave wave can have straight line do to interferece
pray makes a stationary wave form, the droplets show the shape

f = 8.2 Hz

6)
A parallel to T B perpendicular to T
a = 0.68 m per s(sq) towards O (eq position

compare the 2 putting in terms of g, gettin g - 10m per s(sq)

7)change in wave lenght due to motion of source
galaxies are mobing away from us, universe expanding gives evidence for big bang

v = 2.8 x 10^8

critical density is density required to cause big cruch

8)
photon releases one electron, wave would allow energy build up
photon enerfy proportional to freq, lower freq have lower enegery photons with not enough eneergy to relase and electron again wave would allow enegrey to build up
5. I Just Love It Wen I'm The First 2 Make A Thread .... Hehe
6. you had to argue it in terms of light not galaxies.
1x10^-6 = infra red

for frequency i got 16.3, half ppl got that half of peeps got your answer 8.2hz. Overall, there isn't too much difference between answers, so hopefully we all did quite well.
7. (Original post by tktaylor6)

4) amplitude = max distance from center of oscilations
2 cm
2.5 cm
1.6 cm
I THINK IT SHUD HAVE BEEN -1.6CM ...IT ASKED FOR THE DISPLACEMENT WHICH IS A VECTOR QUANTITY ..DNT KNW?
8. i got 1.6cm as it was positive.

1.6cm + [-1.6cm= 0cm as you needed to add them up to make 0cm i think. [i think it was this part, not sure but i did get 1.6cm ].
9. O Crap...was The Progressive Wave Above Or Below????
10. (Original post by mackin boi)
I THINK IT SHUD HAVE BEEN -1.6CM ...IT ASKED FOR THE DISPLACEMENT WHICH IS A VECTOR QUANTITY ..DNT KNW?
Sorry to say this again but it was 1.6cm. The stationary wave was at 0 and the other was at -1.6 giving 1.6cm
11. I did it above...

for the frequency question I thought each square represented 0.25 meant that I multiplied it by four, but I'm clearly wrong, because no one else did.. I also forgot to take two things, i guess that 2 or 3 marks gone... (I'll prob get a mark for the equation tho)

1) changing direction therefore change in accel so must have resultant force from f=ma.
w= 7.3 x10^-5 rad per sec
f=2.03 N
f =586.6N
All except I added the 2.03 on to 586.6... f=mg didn't seem enough for 3 or 4 marks
12. it wasnt f = mg u had to do the cetripetal force = mg -R and then find R
13. (Original post by tktaylor6)
it wasnt f = mg u had to do the cetripetal force = mg -R and then find R
eh?

You've lost me there... R??

What R?

I'm having a mind blank
14. (Original post by MBR50)
eh?

You've lost me there... R??

What R?

I'm having a mind blank
R is the reaction force.

F = mg - R (since F is the resultant force)

so R = mg - F
= 60 x 9.81 - 2 = 587N

... I think
15. I thought it was harder...

was it me or wasnt plancks constant listed?
16. read your text book, the force a scales is the reaction force on it, think of a man on scaled in a falling lift, its how they explain it in the book, my explination is poor but alot of my mates got that same answer and it seemed all that could be done really
17. (Original post by sonja)
R is the reaction force.

F = mg - R (since F is the resultant force)

so R = mg - F
= 60 x 9.81 x 2 = 587N

... I think
but aren't centripetal force and weight both acting downwards.. hence F=mg + 2.03
18. u never had to use plancks constant dude
19. centripetal force is the total resultant force not a force itself man!
20. (Original post by MBR50)
but aren't centripetal force and weight both acting downwards.. hence F=mg + 2.03
Yes they both act downwards. But the centripetal force is the resultant force, of both the weight and the reaction. Hence (taking downwards to be positive) centripetal force = weight - reaction force.

I'm not entirely sure about that though.

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