Math Is Fun Forum

Hello,
i have some 20mm diameter round tubing (conduit) and a bender that has a former of i think 100mm radius. i set a mark on the former where the bend starts or just before the bend.
what i would like to know is how to get a multiplier for the length of conduit.
american benders use a multiplier to work out the length of conduit to get from one place to another and include a bend.
say i wanted to have a run of conduit along a worktop, straight for about 2 foot, then go up an angle of 45 degrees, to go over a 6 inch item. then continue straight for another foot. is there a way to work out the total length of that piece?
this is what i am stuck on. in the uk we use metric but i put this example in feet.
i am using uk equipment which is not the same as american.

hello

i have a parallel rlc circuit which seems to be inductive with a 1 amp magnitude(?)
the circuit is explained in a post below about rlc circuits in parallel with complex numbers.
i havent drawn a phasor diagram. the capacitor and resistor currents are really low, in the micro amps with the inductor at 1 amp which is the supply current. so i am guessing that the phasor diagram would be the voltage pointing to 3 oclock and the current pointing toward 12 oclock, the voltage would have a magnitude of 10(volts, the supply voltage) and the current would have a magnitude of 1 amp(the supply current).
would this be correct. i have read a few things on the internet but not to sure if i have grasped the idea.

thanks

simon

hello
i have a problem  i have this

I =  5*10^-5/1+(2*10^-2) * s = ?

i dont know s, that shouldnt matter.

i think this equals (5*10^-3) 1/200+s

i have done this on latex but cant post it so this will probably look weird, its laplace transform.
i have to rearrange to find I
any help would be great

thanks

simon

hello

I have a circuit with values
v1 = 20 + j0
r1 = 15 +j0
l1 = 0 +j10
c1 = 0 - j5

I have to use superposition and division of complex conjugate numbers.
the resistor, inductor and voltage source are in series. the capacitor is in parallel with the voltage source

I added the resistor and inductor, (15 + jo) + (0 + j10) = 15 + j10, find the conjugate of this 15 - j10
so then product over sum for the components that are in parallel. the inductor/resistor || capacitor

    (0 - j5)*(15 - j10)
(15 + j10)*(15 - j10)

for the numerator I got

0 x 15 = 0
0 x -j10 = 0
-j5 x 15 = -j75
-j5 x -j10 = (j^2)50 = -50   minus 50 because of (j^2) = -1

so the result is -50 -j75, which im not sure about

then the second line

15 x 15 = 225
15 x -j10 =-j150
j10 x 15 = j150
j10 x -j10 = -(j^2)100,    (j^2) = -1 x -100 = 100

225 -j150 +j150 +100, the middle terms cancel leaving 225 + 100 = 325

so I have,     -50 -j75/325

then I divide each of the numerator by the denominator so,

-50/325 = -0.153846

-75/325 = -0.230769

I think I can use this to find polar notation r and theta(the zero with a line through)

im not sure if any of this is right though, any help would be great thanks

simon

hello

I have these two questions

c)    Plot a graph of the kinetic energy of the mass against time. Explain your calculations and state formulae used.

d)    Plot a graph of the kinetic energy of the mass against distance. Explain your calculations and state formulae used.

I have used this formula for the first one,
Ek = ½ mv2 = ½ ma2t2         
Ek is proportional to t2.

this for the second
Ek = ½ mv2 , but we can substitute, giving
Ek = mgy

in not too sure how to show the graphs, but is the above formula along the right lines?
also I have to explain the use of the formula. I think this is just explain why I used it and any transposing required. if anyone knows a better answer for this one please give some advice.

taken from here, http://colourpoint.co.uk/sample_files/physics_as.pdf

this is the first part of the question,

A horizontal force of 80 N acts on a mass of 6 kg resting on a horizontal surface.  The mass is initially at rest and covers a distance of 5 m in 0.92 s under the action of the force.  Assuming there are no energy losses due to air resistance and therefore that the acceleration is constant:

a)    Calculate the total energy expended in the acceleration, I got 11.81 acceleration

b)    Calculate the coefficient of kinetic friction between the mass and the surface.  Suggest materials from which the block and table might be made in order to give such results.  I got 0.155

thanks
simon