Physics 101, Okay, Im not sure what Im doing wrong. Im using fy, 35cos(45) fx, 35sin(43) Not too sure how to find F. help?

2014-10-01 4:25 pm

回答 (3)

2014-10-01 5:25 pm
✔ 最佳答案
What you have in the diagram is a right triangle, where the fy component intersects the fx component at a 90 deg angle. And that makes F = sqrt(fx^2 + fy^2) the hypotenuse. You best reread about the right triangle and the Pythagorean equation.

So we can employ the trig relationships to find F = fy/sin(theta) = 35/sin(radians(45))) = 4.9497E+01 = 49.5 units. ANS.

But here's where you err. fy, 35cos(45) fx, 35sin(43) are not correct. That 35 is in fact fy = 35 as given. So you really have fy = F sin(theta) to solve for F = fy/sin(theta).
2014-10-01 11:39 pm
fy = 35 = F*sin(45) = F*sqrt(2)
F = 35/sqrt(2) = (35/2)*sqrt(2) <<<
2014-10-01 11:36 pm
I don't know what you mean by the commas in "fy, 35cos(45) fx, 35sin(43)"
Here's how I do it.
Fy = 35 = F*sin(45)
Solving for F,
F = 35/sin(45) = 49.5 units long

Additional explanation. I've done so many of these I may have taken too big a jump for you.
sine = opposite / hypotenuse
the opposite is a dotted line -- it is the same length as what the drawing calls Fy. The hypotenuse is F. So
sin(45) = 35/F
Cross-multiplying gets you F*sin45 = 35


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