[SOLVED] Torque Problem

• Oct 3rd 2009, 03:44 PM
matt3D
[SOLVED] Torque Problem
Hello, the question I'm trying to complete states: A wrench 0.1 meters long lies along the positive y-axis, and grips a bolt at the origin. A force is applied in the direction of http://webwork2.math.csufresno.edu/w...23a7a22bf1.png at the end of the wrench. Find the magnitude of the force in newtons needed to supply 100 newton-meters of torque to the bolt.
So far I know, $r=.1m, \tau=100Nm \ and \ |\tau|=|r \times F|=|r||f|\sin\theta$
So I need to find F right? But why does the problem give me a force already? Do I have this problem set up correctly?

Thanks,
Matt
• Oct 4th 2009, 03:00 PM
matt3D
anybody? this problem is making me go (Headbang) lol
• Oct 4th 2009, 05:47 PM
skeeter
Quote:

Originally Posted by matt3D
Hello, the question I'm trying to complete states: A wrench 0.1 meters long lies along the positive y-axis, and grips a bolt at the origin. A force is applied in the direction of http://webwork2.math.csufresno.edu/w...23a7a22bf1.png at the end of the wrench. Find the magnitude of the force in newtons needed to supply 100 newton-meters of torque to the bolt.
So far I know, $r=.1m, \tau=100Nm \ and \ |\tau|=|r \times F|=|r||f|\sin\theta$
So I need to find F right? But why does the problem give me a force already?
it didn't ... it gave you a torque

$\vec{r} = <0,0.1,0>$
$\vec{F} = <0,-5F,-4F>$

$\vec{\tau} = \vec{r} \times \vec{F} = -0.4F \vec{i}$

$0.4F = 100 Nm$

$F = 250 N$
• Oct 4th 2009, 10:38 PM
matt3D
Quote:

Originally Posted by skeeter
$\vec{r} = <0,0.1,0>$
$\vec{F} = <0,-5F,-4F>$

$\vec{\tau} = \vec{r} \times \vec{F} = -0.4F \vec{i}$

$0.4F = 100 Nm$

$F = 250 N$

Thank you skeeter. That makes sense. I put in 250N but the answer was still incorrect, but once I realized it wanted the magnitude, I just plugged in 250 to the direction of the force took it's magnitude and got 1600.78N and it was correct. Thanks again!