Wednesday

April 23, 2014

April 23, 2014

Posted by **Natalie** on Friday, November 9, 2012 at 5:07pm.

Hmm, (this is essentially just a vector problem) I know you're supposed to find the position vector r and take the cross product of r x F, the force vector, for the torque vector. What I seem to be having trouble with is understanding how to come up with the position vector. So I thought that you're applying the force at point (3, 0, 0), but you want to put the rotation axis at (-1.3, 2.4, 0), and thus the position vector r would be the vector "from" the point (-1.3, 2.4, 0) "to" the point (3, 0, 0) (instead of just say (3, 0, 0 if it the center was at the origin). I'm pretty sure you can simply subtract: (-1.3, 2.4, 0) - (3, 0, 0) = (-4.3, 2.4, 0), and that's your position vector r. And so the cross product should be:

r x F =

i j k

(-4.3, 2.4, 0)

(0.8, 2.5, 0)

r x F = 0i + 0j + (-4.3*2.5 - 0.8*2.4)k = -12.67k = (0, 0, -12.67)

I'm not sure that this is right though, I tried it in a homework program and it says this is incorrect, any tips, I'm sure I'm just missing some simple thing :(.

- Physics or Math -
**Jennifer**, Friday, November 9, 2012 at 5:11pmThe torque is about the point (-1.3, 2.4), so treat this as your origin,. . .

This makes the r vector (4.3, -2.4, 0)

- Physics or Math -
**Natalie**, Friday, November 9, 2012 at 5:16pmI thought maybe I mixed up the order, and that I should have done (3,0,0) - (-1.3,2.4,0), point minus "effective origin" (the rotation axis) which makes more sense, this changes it to 12.67k, is that correct?

- Physics or Math -
**Natalie**, Friday, November 9, 2012 at 5:16pmYay thanks, thought it was simple thank you.

**Related Questions**

physics - A crate is pulled to the right with a force of 84.5 N, to the left ...

physics - A craet is pulled right with a force of 82.0 N to the left with a ...

math - How much force is needed to accelerate a 50-kg rider and her 250-kg ...

Physics - A crate is pulled right with a force of 82.0N to the left wtih a force...

Physics - Which is the strongest fundamental force acting between microscopic ...

PHYSICS. HELP! - I've been stuck on this physics homework since I got home. I ...

physics (vector) - the force f1 and f2 are acting on a body one force is double ...

physics - a physics book is on top of a drafting table at 35 degree angle. Find ...

Physics - You push your couch a distance of 3.8 m across the living room floor ...

Physics -please help - This is for my earth science class I have not had physics...