SRL Archive - Mathematics

Pre-calc final is in two days and I have a question that I would greatly appreciate help on.

Question: Suppose that a bolt has its axis along the z-axis. A force of 5i + 2j acts at a displacement of d = 7i + 10j. Find the torque vector. In what direction does the torque vector point?

Not exactly part of the question, but for those who know how to do this in terms of physics, the force is the moment arm and the displacement tells the location of the pivot point I think.

My understanding: I have the formula F x D = T (F and D are vectors and I'm not sure about T. My notes are shitty.) So do I do the cross product of 5i + 2j + 0z and 7i + 10j + 0z, or are the coefficients of J different? How do I describe the direction when I get the vector from the cross product? From googling I saw that in physics something called the Right Hand Rule is used to determine the direction of torque, but I didn't understand this and I don't know if this is how I would describe it in a pre-calc class. Please also keep in mind that I've never actually done any of these type of problems and my book doesn't cover them.

I would really appreciate any help that you can give quickly. I also have MSN if you're good at math and would be willing to help me some more. [email]Bbrian@live.com[/email]

right-hand rule: make your right hand into a thumb's up, point your thumb along the torque vector and the rest of your fingers show in which direction the body will rotate.

Yes since T = F x D, you need to do the cross product of the force and direction vectors. Make sure you take F (cross) D and NOT D (cross) F. And like you and Yakman stated use the right hand rule to determine the direction.

If you need more help with the Right hand rule or a cross product let us know.