Homework_16

Homework_16 - Nguyen, Thanh Homework 16 Due: Nov 2 2007,...

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1 This print-out should have 10 questions. Multiple-choice questions may continue on the next column or page – fnd all choices beFore answering. The due time is Central time. 001 (part 1 oF 2) 10 points A particle is located at the vector position ~r = (2 . 3 m)ˆ ı + (4 . 3 m)ˆ and the Force acting on it is ~ F = (2 . 9 N)ˆ ı + (1 . 4 N)ˆ  . What is the magnitude oF the torque about the origin? Correct answer: 9 . 25 N m. Explanation: Basic Concept: ~ τ = ~r × ~ F Solution: Since neither position oF the par- ticle, nor the Force acting on the particle have the z -components, the torque acting on the particle has only z -component: ~ τ = [ x F y - y F x ] ˆ k = [(2 . 3 m) (1 . 4 N) - (4 . 3 m) (2 . 9 N)] ˆ k = [ - 9 . 25 N m] ˆ k . 002 (part 2 oF 2) 10 points What is the magnitude oF the torque about the point having coordinates [ a, b ] = [(3 m) , (7 m)]? Correct answer: 6 . 85 N m. Explanation: Reasoning similarly as we did in the pre- vious section, but with the di±erence that relative to the point [(3 m) , (7 m)] the y - component oF the particle is now [ y - (7 m)], we have ~ τ = { [ x - a ] F y - [ y - b ] F x } ˆ k = { [(2 . 3 m) - (3 m)] [1 . 4 N] - [(4 . 3 m) - (7 m)] [2 . 9 N] } ˆ k = { 6 . 85 N m } ˆ k . keywords: 003 (part 1 oF 1) 10 points Consider vectors ~ A and ~ B with coordinate components shown in the illustration below. A B An isometric drawing: Each coordinate has a length oF ± 5 units. To indicate the coordinates oF each vector, a line is projected to the hor- izontal plane then two lines are pro- jected to the horizontal coordinates. As well, a line is directly projected to the vertical coordinate. What is the magnitude oF the vector prod- uct k ~ A × ~ B k oF these two vectors? Correct answer: 24 . 7184 units 2 . Explanation: Basic Concept: ~ A × ~ B = f f f f f f ˆ ı ˆ ˆ k A x A y A z B x B y B z f f f f f f (1) = f f f f A y A z B y B z f f f f ˆ ı + f f f f A z A x B z B x f f f f ˆ + f f f f A x A y B x B y f f f f ˆ k = ( A y B z - A z B y ı + ( A z B x - A x B z + ( A x B y - A y B x ) ˆ k Let : A

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This note was uploaded on 10/24/2011 for the course PHYS 1710 taught by Professor Weathers during the Winter '08 term at North Texas.

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Homework_16 - Nguyen, Thanh Homework 16 Due: Nov 2 2007,...

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