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# Physics Homework question?

A 1.7 kg ball on the end of a lightweight rod is located at (x, y) = (4.0 m, 3.0 m), where the y-axis is vertical. The other end of the rod is attached to a pivot at (x, y) = (0 m, 4.0 m). What is the torque about the pivot? Express your answer using unit vectors. Best answer awarded

### 1 Answer

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- JOHNLv 73 weeks agoBest answer
Length of rod = √((4 – 0)² + ((3 – 4)²) = √17

i, j, k are unit vectors in the x-, y-, z-directions

Vector torque of ball about pivot is

(mgl)(-k) = 1.7 x 9.8 x √17 (-k) (using a right-handed

coordinate system)

= - 68.7k Nm.

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