math (vectors) & physics

Posted by sam on Wednesday, March 28, 2007 at 7:32pm.

In unit-vector notation, what is the net torque about the origin on a flea located at coordinates (-2.0, 4.0 m, -1.0 m) when forces F1 = (-4.0 N) k and F2 = (-5.0 N) j act on the flea?

For Further Reading

* math (vectors) & physics - drwls, Thursday, March 29, 2007 at 12:13am

Torque is the cross product of the radius vector and the net force vector. In three dimensions, it can be computed as fallows.
|i... j... k|
|0... -5... -4|
|-2... 4... -1|

Compute the determinant


this is what i've done and im stuck.

= i[(-5)(-1)-(-4)(4)] + j[(-4)(-2)-(0)(-1)] + k[(0)(4)-(-5)(-2)]

= 21i + 8j - 10k

and that's the wrong answer.. .what am i doing wrong? help?

***there's an example in my book of a similar problem with different numbers:
-In unit-vector notation, what is the net torque about the origin on a flea located at coordinates (0, –4.0 m, 5.0 m) when forces F1=(3.0 N)k and F2=(-2.0 N)j act on the flea?
~~~~~and the answer to that question is: (–2.0 i) N · m

I agree wth your numbers. However if the right hand rule is used for torque, then it should have been F x R instead of R X F. This would change the sign of the answer.

  1. 👍
  2. 👎
  3. 👁

Respond to this Question

First Name

Your Response

Similar Questions

  1. physics

    A plum is located at coordinates (-4.0 m, 0.0 m, 6.0 m). In unit-vector notation, what is the torque about the origin on the plum due to force F whose only component is indicated by each of the following equations? (a) Fx = 8.0 N

  2. Physics

    A car travels at 80 km/h on a level road in the positive direction of an x axis. Each tire has a diameter of 66 cm. Relative to a woman riding in the car and in unit-vector notation, what are the velocity at the (a) center, (b)

  3. Math: Vectors

    Find any vector w that is perpendicular to both vector "u = 3j + 4k" and vector "v = 2i". Note: i, j and k are unit vectors How would you solve this problem? Please walk me through?

  4. Math Riddle

    What day would yesterday be if Wednesday was five days before the day after tomorrow? pLEASE HELP ME WITH THE RIDDLE i POSTED!!!!!! EARLIER waht materials could upumuse Alright already! I really wondered why you just didn't pick

  1. physics

    Vector V represents a displacement of 120 km at 29.0 degrees counterclockwise from the x axis. Write V in unit vector notation. Express your answer using three significant figures. V= _______ km i know the answer should be

  2. science (physics) Need to solve this today please

    (a) Express the vectors A, B, and C in the figure below in terms of unit vectors. (b) Use unit vector notation to find the vectors R = A + B + C and S = C – A – B. (c) What are the magnitude and directions of vectors R and S?

  3. physics calc based

    In the product F = qB (vectors), take q = 2 (neglecting the units of charge, q) and v = 2.0 i + 4.0 j + 6.0 k and F = 4.0 i + (-20 j) + 12 k . What then is B in unit-vector notation if Bx=By ?


    In Figure below, an electron accelerated from rest through potential difference V1=0.955 kV enters the gap between two parallel plates having separation d = 18.2 mm and potential difference V2= 160 V. The lower plate is at the

  1. Physics - drwls

    Posted by winterWX on Monday, March 19, 2007 at 11:51pm. A 2600 kg truck traveling north at 38 km/hr turns east and accelerates to 55 km/hr. What is the change in the truck's kinetic energy? What is the magnitude of the change in

  2. Physics

    Vector A has a magnitude 12m and is angled at 60 degrees counterclockwise from the positive direction of the x axis of an xy coord. system. Also. Vector B = (12m)i + (8m)j on that same coord system. Rotate the system

  3. Physics

    A particle is in uniform circular motion about the origin of an xy coordinate system, moving clockwise with a period of 3.50 s. At one instant, its position vector (from the origin) is r = (8.00 m) ihat - (7.00 m) jhat. At that

  4. cartesian vectors 2

    let vector U = (vector u1, vector u2) vector V = (vector v1, vector v2) and vector W = (vector w1, vector w2) Prove each property using Cartesian vectors: a) (vector U+V)+W = vector U+(v+W) b) k(vector U+V) = k vector U + k vector

You can view more similar questions or ask a new question.