# Physics problem

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#1
Can anyone help with this problem?
A young radio amateur maintains a radio link with two girls living in two towns. He positions an aerial array such that when the girl living in town A receives a maximum signal, the girl living in town B receives no signal and vice versa. The array is built from two uniform rod aerials transmitting with equal intensities in all directions in the horizontal plane.
a) Find the parameters of the array ie the distances between the rods, its orientation and the phase shift between the electrical signals supplied to the rods, such that the distance between the rods is minimum.
b) Find the numerical solution of the boy has a radio station transmitting at 27MHz and builds up the aerial array at Portoroz. Using a map he has found that the angles between the north and the direction of A (Koper) and of B (small town of Buje in Istria) are 72° and 157° respectively.
Any help would be greatly appreciated.
Thank-you.
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#2
Here's another one;
In a space research project, two schemes of lauching a space probe out of the solar system are dicussed. The first scheme (i) is to launch the probe with a velocity large enough to escape from the solar system directly. According to the second one (ii), the probe is to approach the one of the outer planets, and with its help change direction of motion and reach the velocity necessary to escape from the solar system. Assume that the probe moves under tha gravitational field of only the sun or the planet depending on which is stronger at that point.
a) Determine the minimum velocity and its direction relative to the earth's motion that should be given to the probe on launching according to scheme (ii)
b) Suppose a probe has been launched in the direction determined in a) but with another velocity. Determine the velocity of the probe when it crosses the orbit of Mars, ie, its parallel and perpendicular components with respect to this orbit. Mars is not near the point of crossing when crossing occurs.
c) Let the probe enter the gravitational fiels of Mars. Find the minimum lauching velocity from the earth necessary for the probe to escape from the solar system.
Hint: From the results a) you know the optimal magnitude and the direction of the velocity of the probe that is necessary to escape from the solar system after leaving the gravitation field of Mars. (You do not need to worry about the precise position of Mars during the encounter.) Find the realtion between this velocity and the velocity compenents before the probe enters the gravitational field of Mars, ie, the components determined in b). what about the conservation of energy of the probe?
d) Estimate the fractional saving of energy in scheme (ii) with respect to scheme (i)
Notes: Assume that all the planets evolve around the sun in circles, in the same direction and in the same plane. Neglect air resistance, the rotation of the earth around its axis as well as the energy used in escaping from the earth's gravitational field.
Data: Velocity of the earth around the sun is 30km/s and the ratio of the distances of the earth and Mars from the sun is 2/3

Thank you very much for any help, I don't need a perfect solution, just some pointers for where to start.
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16 years ago
#3
You scare me........
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#4
(Original post by bono)
You scare me........
why?
0
16 years ago
#5
don't worry about him, hes just an *******
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#6
(Original post by DazYa)
don't worry about him, hes just an *******
That's nice, but how does it help solve my physics problems?
0
16 years ago
#7
i cant help you because ive never done that before in physics
sorry
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#8
(Original post by DazYa)
i cant help you because ive never done that before in physics
sorry
I haven't done this stuff either, that's part of the problem. Theoretically they can be solved just using mostly A level stuff...
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16 years ago
#9
do you assume that the intensity does not follow an inverse square relationship for the first one?
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#10
(Original post by grandpaw)
do you assume that the intensity does not follow an inverse square relationship for the first one?
Does that make much of a difference? My physics teacher said the first question could be about interference. Beyond that, I'm stumped.
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16 years ago
#11
(Original post by sazzles)
Does that make much of a difference? My physics teacher said the first question could be about interference. Beyond that, I'm stumped.
it does make a difference, because if the two sources are in two different positions, with an inverse square relationship they will not completely cancel (because the distances to a point will not be the same, and so the intensities will not be equal and opposite)
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#12
(Original post by grandpaw)
it does make a difference, because if the two sources are in two different positions, with an inverse square relationship they will not completely cancel (because the distances to a point will not be the same, and so the intensities will not be equal and opposite)
I see, so you would have to suppose that the intensity doesn't drop off significantly. I hadn't thought that complicatedly.
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16 years ago
#13
(Original post by sazzles)
I see, so you would have to suppose that the intensity doesn't drop off significantly. I hadn't thought that complicatedly.
you can approximate that the distance to the two towns is so large compared to the distance between the two aerials that it doesnt really matter
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#14
(Original post by grandpaw)
you can approximate that the distance to the two towns is so large compared to the distance between the two aerials that it doesnt really matter
Can you clarify? What doesn't matter? The distance between the two aerials?
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16 years ago
#15
(Original post by sazzles)
Can you clarify? What doesn't matter? The distance between the two aerials?
if the distance between the two aerials is small compared to the distance to the town, the distances to the town will be roughly the same, and the fractional difference in intensity of the two signals will be insignificant, so they will effectively cancel.
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#16
(Original post by grandpaw)
if the distance between the two aerials is small compared to the distance to the town, the distances to the town will be roughly the same, and the fractional difference in intensity of the two signals will be insignificant, so they will effectively cancel.
Oh I get it now. Thanks for all the help, you're 10 times more useful than my physics teacher.
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16 years ago
#17
(Original post by sazzles)
Oh I get it now. Thanks for all the help, you're 10 times more useful than my physics teacher.
well, in my day, physics teachers knew a bit about physics.
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#18
(Original post by grandpaw)
well, in my day, physics teachers knew a bit about physics.
My physics teacher used to be a PE teacher!
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#19
Hey all you clever people who know lots of physics, if you can offer any more inspiration for how to tackle these problems, it would be greatly appreciated. Thank you muchly in advance.
0
16 years ago
#20
(Original post by sazzles)
Can anyone help with this problem?
A young radio amateur maintains a radio link with two girls living in two towns. He positions an aerial array such that when the girl living in town A receives a maximum signal, the girl living in town B receives no signal and vice versa. The array is built from two uniform rod aerials transmitting with equal intensities in all directions in the horizontal plane.
a) Find the parameters of the array ie the distances between the rods, its orientation and the phase shift between the electrical signals supplied to the rods, such that the distance between the rods is minimum.
b) Find the numerical solution of the boy has a radio station transmitting at 27MHz and builds up the aerial array at Portoroz. Using a map he has found that the angles between the north and the direction of A (Koper) and of B (small town of Buje in Istria) are 72° and 157° respectively.
Any help would be greatly appreciated.
Thank-you.
Its a while since ive done the waves and nuclear phyics module - but the formulas youll need to use are:

y = (Lambda)D/d

or/and

n(Lambda) = dsinx

Did you not get any data for the first part of the question?
0
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