Torque problems

  1. I'm stuck on these problems!

    1. Suppose a 90.0-g mass is placed at the 82.0 cm mark of a 120.0 g uniform meterstick. At what mark will the meterstick balance?

    For this problem, I did TCCW=TCW. I think the TCW is (90 g)*(9.8 m/s^2)*(32 cm). For TCCW, I am not sure because I do not know where the pivot point is.

    2. A 10,000 kg bridge of length 10 m is supported at both ends. If a 2000-kg car is parked on the bridge 3.0 m from the left support, what are the supporting forces at the left and right ends?

    I drew a diagram for this problem, but I do not know how to calculate the supporting forces.
     
  2. jcsd
  3. set up the momentum balance about the zero mark of the meterstick:
    90*9.8*82+120*9.8*50-210*9.8*x=0
    210 (=90+120)*9.8 being the reaction force at the pivotpoint
    x = the distance of the pivot point from the zero mark
    work out x and you have the answer for question 1.
     
  4. Doc Al

    Staff: Mentor

    bridge problem

    Identify all the forces acting on the bridge: its weight, the weight of the car, the left supporting force, and the right supporting force. Draw these on your diagram.

    Now apply the conditions for equilibrium:
    (1) The forces must balance
    (2) The torques about any point must balance

    Give it a shot.
     
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