1. ## [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 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, $\displaystyle r=.1m, \tau=100Nm \ and \ |\tau|=|r \times F|=|r||f|\sin\theta$
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

2. anybody? this problem is making me go lol

3. 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 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, $\displaystyle r=.1m, \tau=100Nm \ and \ |\tau|=|r \times F|=|r||f|\sin\theta$
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

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

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

$\displaystyle 0.4F = 100 Nm$

$\displaystyle F = 250 N$

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

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

$\displaystyle 0.4F = 100 Nm$

$\displaystyle F = 250 N$
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!