two mothers...(food for thought) (1 Viewer)

[superhubert]

i've got two practice q's from space and motors for the game,
i can't get the same answer as the given solutions. any ideas?

1.an aircraft can withstand the stresses of a 15g acceleration (ie an acceleration 15 times that of gravity), then what is its minimum turning radius at a speed of 900km/h?

this one seems simple enough (i'm prbably just doing something stupid) but can anyone get an answer of 425m?

2. heres the mother.......
A long straight wire carries a constant current in a uniform magnetic field of 31 micro T directed towards north. At a point 5.2 cm above the wire, the net field strength is zero. what is the magnitude and direction of the current in the wire?
the suggested answer is 8.1A but i seem to get 806A (which i know can't be right. any takers?

 

[Ace-Pilot]

not sure if this is correct,

using this formula a = v^2/r

i got 425m but it dosn't really sound right, whats the correct answer ?

 

[wogboy]

1. I'd assume the answer of 425m should be correct if the plane is turning the circular loop in the horizontal plane in the sky (i.e. gravity has no effect).

r = v^2/a
= (900/3.6)^2 / (15 * 9.8)
~ 425m

2. I think for this question you have to use the formula:

B = kI/d (k = magnetic constant = 2 * 10^-7)

so I = rB/k
= (5.2 * 10^-2 * 31 * 10^-6) / (2 * 10^-7)
~ 8.1 A

Perhaps the mistake you made was not converting 5.2 cm to 0.052m ??

[Edit] As for the direction, if you use the right hand grip rule, you will find the current is going EAST.

 

[superhubert]

thats what i thought when i read the answer..
this is what i got....
a=v^2/r
a=15*9.8
=147
v=900km/h^2
=10497600m
therefore i get a radius of 71412.2449m!
i know that sounds wrong! how'd you get 425m out of the same equation?

 

[wogboy]

You have to convert v from km/h into m/s (3.6 km/h = 1 m/s). So you have to divide it by 3.6 to get the speed in m/s (900/3.6 km/h = 250 m/s).

 

[Ace-Pilot]

yep i did the same thing as wogboy for Q 1, actually 425 does sound right, so when the plane does half a loop it will be aprox 1 km diameter, The reason i thought this is wrong is coz usually a plane can only hack up to 10 - 12 g after that it breaks into pieces. So yeah 425 is right.

 

[superhubert]

stupid mistakes on both......cheers!