Physics

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A person holds an object of mass m = 4.2 kg on the palm of the hand with the arm stretched. Use the torque equilibrium equation to determine the magnitude of the force F exerted by the biceps muscle when a = 25 cm, b = (0.15 · a), and the angle θ = 75°. Neglect the weight of the lower arm

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(a+b)(Fg)-b(Fcosθ) = 0
-->solve for F

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No but I am going crazy trying to do the calculations! Grr...wish I had more time to review before doing this h/w!

Thanks though. If I figure it out i'll post back here, ok

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Hey Anna, can you break that down. I'm so confused!

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Fg in the eqn she gave is mg...

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Did any of you guys find 1 or 3?

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So, basically i wrote down the torque equilibrium equation where torque equals 0 and the point of reference being the one shown in the diagram. The distance from the point of reference to where Fg is applied is a PLUS b since a is just the distance from the point where F is applied...NOT from the point of reference. The signs you can find using the right-hand rule..i used positive as counterclockwise..so torque is pointing towards you.

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Anna if u are having trouble with number 3, have a look at Ex5.2 it will help.

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these are the steps to do number 3. i still have yet to try it though:

first you need all the euations of the forces

so horizontal and vertcal

then you need torque

so once you hv your torque youll hv lots of L

you should factor that out

nd solve for T

then sub T into the horizontal forcees equation

nd solve for Rx

And for Question 2 are we supposed to convert cm to m and when we find b, there's no given units so am i supposed to just multiply it with a and it automatically becomes the same unit as a?

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the units are given.. it's cm throughout..you don't have to convert because the units for l get canceled out in the end anyways

i got an answer around 3000 for #3? Anyone else get something similar?

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yep, it's supposed to be a huge number for #3

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i got around 4000s. Hey for question 2 is it supposed to be a tremendous number as well. I got like 4450

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Did anyone figured out #1?

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No! I've tried multiple ways to do it.. and yet still not getting the right answer. I think I'm messing up my coordiante system and the angles for the forces..

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Question #1

T(l1)cos30 + Warm(l2)cos30 - WM(l3)cos30
solve for T

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time's up..lol

Thanks guys!