Author Topic: Methods question year 11 help? (Read 879 times) Tweet Share

TMJ · « **on:** February 07, 2013, 08:02:48 pm »

Can someone help me with this question?
The bending moment, M, of a simple beam used in a bridge construction is given by the formula M=wlx/2-wx^2/2.
If l=13m, w = 16 kg/m, and M =288kg, calculate the value of x.

BigAl · « **Reply #1 on:** February 07, 2013, 08:05:45 pm »

Chuck it into your calc. And solve the quadratic equation

TMJ · « **Reply #2 on:** February 07, 2013, 08:06:55 pm »

Is it possible to find it by hand?

BigAl · « **Reply #3 on:** February 07, 2013, 08:09:57 pm »

You can find x by using quadratic formula but the numbers are big

Professor Polonsky · « **Reply #4 on:** February 07, 2013, 08:39:56 pm »

If I got your syntax right, it's

$M=\frac{wlx}{2} - \frac{wx^2}{2}$

Substituting the values in gives

$288=104x - 8x^2$

$-8x^2 + 104x - 288=0$

Dividing the equation by $-8$ yields

$x^2 - 13x + 36=0$

Which you can factorise

$(x-9)(x-4)=0$

$x=9$ or $x=4$

BigAl · « **Reply #5 on:** February 07, 2013, 08:49:57 pm »

Quote from: Polonius on February 07, 2013, 08:39:56 pm

If I got your syntax right, it's

$M=\frac{wlx}{2} - \frac{wx^2}{2}$

Substituting the values in gives

$288=104x - 8x^2$

$-8x^2 + 104x - 288=0$

Dividing the equation by $-8$ yields

$x^2 - 13x + 36=0$

Which you can factorise

$(x-9)(x-4)=0$

$x=9$ or $x=4$

To be honest I was too lazy

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Author Topic: Methods question year 11 help? (Read 879 times) Tweet Share

TMJ

Methods question year 11 help?

BigAl

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TMJ

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BigAl

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Professor Polonsky

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