How do i solve this numerically?

[Physicsfan]

A block and tackle system of pulleys is used to raise a load of 500N through a height of 20m.the work done against friction is 2000J.

 

what is the displacement of the effort and the mechanical advantage of the system?

[Mr Skeptic]

As stated, there is not enough info. Perhaps you know how many blocks and tackles there are?

[Physicsfan]

no.

this question appeared in our 9th grade final exams so the question cannot be wrong.

I do not know how many blocks there are because the question does not mention that.

 

the net work done by the effort would be 12000J.

so the efficiency of the system would be 10000J/12000J=M.A/V.R.

Using this relation, is it possible to find the displacement of effort?

[Mr Skeptic]

this question appeared in our 9th grade final exams so the question cannot be wrong.

 

Glad to see someone still has faith in our public education system

 

so the efficiency of the system would be 10000J/12000J=M.A/V.R.

Using this relation, is it possible to find the displacement of effort?

 

Yes, but only if you know the mechanical advantage. If you knew the ratio of forces, the ratio of distances, or the number of pulleys in the rope and tackle system, you could get an answer. Any chance there was a picture or something to go with the words?

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Merged post follows:

Consecutive posts merged

According to the wiki page, http://en.wikipedia.org/wiki/Block_and_tackle

 

friction is an arbitrary 10%. If this applies to your problem, I'm guessing your block and tackle has an ideal M.A. of 2, so that the effort distance would be 40m.

Edited May 13, 2010 by Mr Skeptic
Consecutive posts merged.

[Physicsfan]

If force required to overcome friction was x N, the total effort would be (E+x)N.

so M.A=L/(E+x)=(5/6)*V.R.

=(5/6)*(ideal M.A).

=(5/6)(L/E).

6E=5E+5x

E=5x

now is it possible to solve?

Edited May 14, 2010 by Physicsfan

[Mr Skeptic]

Well, if you know the amount of friction per unit of mechanical advantage, then knowing the total friction gives you the mechanical advantage. The mechanical advantage gives you the distance of the effort, since you know the distance of the resistance.

[Physicsfan]

i can take the net effort to be 6x. So now i get a single variable for effort.

but then again ill have to consider another variable for displacement.