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I have the question:

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"Wire Q is attached to a Newton meter so that the force the wire exerts on the rod can be measured. The reading on the Newton meter is 2.0 N and the weight of the rod is 5.0N.

Calculate:

(i) The force that wire P exerts on the rod.

(ii) The distance d."

For the first part (i) I got 5.0N - 2.0N = 3.0N for wire P.

However, for the second part I am not sure how to find the distance d.

I know that I must multiply the vertical by the horizontal but I am not sure how to do this.

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    Use torque. It should be zero at the center of mass: $-3.0N \times d + 5.0N\times 0 + 2.0N \times (90 cm - d) = 0$. – 2017-01-18
  • 0
    Could you please elaborate ? (: – 2017-01-18

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Try taking moments about the centre of mass.

  • 0
    I am not sure what you mean could you please explain with more detail ? (: – 2017-01-18
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    It is exactly what was mentioned in the comment by @Wood. When you have a body at rest (no motion), you have that there is an equilibrium of forces (condition for no linear motion), and an equilibrium of moments (condition for no angular motion). Since we know that the body is not rotating around the centre of mass, the moments (product of force and perpendicular distance) should be equal on both sides. – 2017-01-18
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    I understand that moment is the force multiplied by the distance however I am still unsure how to find the distance as the solutions say that the answer should be 0.36 m and I am not getting this. Which means I am doing something wrong. – 2017-01-18
  • 1
    At the center of mass we will have moments due to the force exerted by wire P and the force by wire Q. We do not include the force due to the weight of the body since it acts at the centre of mass (and hence has zero moment about this point). Writing the equation for equilibrium of moments gives us: 3 * d = 2 *(90 -d) which gives upon simplification: 5*d = 180 or d = 180/5 = 36 – 2017-01-18
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    Could I just ask how you got 5 * d ? As wouldn't taking 2 to the left hand side make it 3d/2 ? Thanks (: – 2017-01-18
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    3 * d = 2*90 - 2 * d which gives 3*d + 2*d = 2*90 – 2017-01-19
  • 1
    Let us [continue this discussion in chat](http://chat.stackexchange.com/rooms/52035/discussion-between-bolutife-ogunsola-and-dan). – 2017-01-19
  • 0
    I have posted another question could you please help me with that also ? (: – 2017-01-19