Sam G. answered • 05/05/15
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Since this is a multiple choice question, lets compare the pulleys to planets.
The larger the planet (diameter) the slower the speed of rotation. (Earth takes longer than mercury to spin).
Okay back to pulleys.
The first pulley has a smaller diameter, and turns at 150rev/min.
The second pulley has a larger diameter, we don't know the speed yet, but we can conclude that since it is larger, it must be slower in speed. So say goodbye to choices c and d.
Now set up a basic proportion.
Diameter=(3mm/5mm)=(150rev/x)=Revolutions
But remember! SPEED AND DIAMETER ARE INVERSELY RELATED, diameter goes up, speed goes down.
So flip the revolutions fraction.
(3mm/5mm)=(x/150rev)
Cross multiply the proportion
3mm(150rev)=(5mm)(x)
Essentially you have:
5x=450
Divide both sides by 5, to solve for x.
x=90revs.
If you didn't flip the revolutions fraction , you'd end up with 250, which we established earlier is not correct!
Inverse relationships are shown by
(3mm)(150revs)=5mm(xrevs)
you could also solve for x this way, by dividing 5 by both sides, gets you 90. Whichever works, but it's about understanding!
Sam G.
Inversely related components, yes.
If they were directly related, as far as the end part goes of my answer, you would place them on opposite sides of the = sign.
So indirectly related components xy compared to x1y1,
Set it up to be xy=x1y1
Directly related components xy compared to x1y1
Set it up to be xx1=yy1.
In this case doing it my way, you would not flip the fraction if Directly related.
Hope that clears things up!
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05/05/15
Sofia G.
05/05/15