Physics or Math

posted by .

A force F = 0.8 i + 2.5 j N is applied at the point x = 3.0 m, y = 0 m. Find the torque about the point x = -1.3 m, y = 2.4 m.

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 -

    The 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 -

    I 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 -

    Yay thanks, thought it was simple thank you.

Respond to this Question

First Name
School Subject
Your Answer

Similar Questions

  1. physics- torque

    1. Find the magnitude of the torque produced by a 3.0 N force applied to a door at a perpendicular distance of 0.25 m from the hinge. 2. A simple pendulum consists of a 3.0 kg point mass hanging at the end of a 2.0 m long light string …
  2. Physics

    A body is pivoted at a Point O. Three forces act on it in the directions shown on the figure. FA = 11 N at point A, 8.0 m from O. FB = 15 N at point B, 4.0 m from O. FC = 20 N at point C, 3.0 m from O. What is the net torque about …
  3. physics

    In the figure, forces A, B, C and D each have magnitude 50.0 N and act at the same point on the object. What torque (magnitude and direction) does A force exert on the object about point P?
  4. physics

    A force, F = (2x + 5y) N, is applied to an object at a point whose position vector with respect to the pivot point is r = (2x + 4y + 5z) m. Calculate the torque created by the force about that pivot point.
  5. Physics

    A force, F = (3x + 4y) N, is applied to an object at a point whose position vector with respect to the pivot point is r = (3x + 3y + 3z) m. Calculate the torque created by the force about that pivot point. I know that torque = -12x …
  6. physics

    I am studying for a physics exam and this is the pretest. There are some that I don't understand. If someone could help me get to the answer (show all the work so I can look it all over) that would be AMAZING! Thank you very much! …
  7. physics

    A force in the +y direction applied at the point x=2.3m,y=1.4m gives rise to a torque of 39n*m about the origin. Find the magnitude of the force.
  8. College Physics

    A force, F = (2x + 3y) N, is applied to an object at a point whose position vector with respect to the pivot point is r = (5x + 4y + 2z) m. Calculate the torque (in units on Nm) created by the force about that pivot point.
  9. Physics

    A 49-N force is applied perpendicular to the portion BC of the bent bar. Determine the moment of P about point B and about point A. The image shows a bar that is straight from point A to B but then bends at a 42 degree angle to the …
  10. Physics

    A force, F = (6x̂ + 7y hat) N, is applied to an object at a point whose position vector with respect to the pivot point is r = (7x̂ + 7y hat + 7ẑ) m. Calculate the torque created by the force about that pivot point.

More Similar Questions