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7 Pre-Lab Questions

  1. Mar 20, 2008 #1
    1. The problem statement, all variables and given/known data
    The condition ∑ Fi = 0 is not sufficient to assure that a rigid body is in equilibrium.


    2.A quantity that expresses how a force can create an angular acceleration is called

    a. moment of inertia
    b. angular influence
    c. angular energy
    d. angular momentum
    e. torque

    According to the lab manual, clockwise torques are taken as Fill in the Blank 01 (positive or negative) and counterclockwise torques are taken as Fill in the Blank 02 (positive or negative).

    Calculate the lever arm of F as measured from the point O. The angle is θ = 42o and the distance r = 1.5 m. Express the answer in meters.

    Lever Arm.bmp
    Save Answer

    5.Given the situation in the figure below. The mass m1 is 0.55 kg and it is located at x1 = 30 cm. The pivot point is represented by the solid triangle located at x = 45 cm. The mass of the meter stick (mms = 0.40 kg) is located at its geometric center, xms = 50 cm. The mass m2 is 0.35 kg and it is located at x2 = 80 cm. Calculate the net torque (in N⋅m with the proper sign) due to these three weights. Use g = 9.8 m/s2.

    Torque Figure.bmp

    6. The apparatus described in Question 5 is in equilibrium.


    7.Suppose that a meter stick is balanced at its center. A 0.17-kg is positioned at 31 cm from the left end of the meter stick. Where should a 0.26 kg mass be placed to balance the 0.17 kg mass? Express your answer in terms of the position (in cm) of the 0.26-kg mass as measured from the left end of the meter stick.

    2. Relevant equations
    Hey guys my proffesor gave us some questions he reccomended to attempt doing before tommorow's lab. I have finished them but we do not have answers so i was wondering if you guys could tell me if i was doing anything wrong.

    3. The attempt at a solution
    Here are my answers:
    2.Angular momemtum
    3.positive(counterclockwise) and negative (clockwise) used right hand rule
    4. I got -.599 by using rcos(theta) --i really dont know how to do this one
    5.-.098 using T=Fr
    Any help appreciated thanks alot guys!
    Last edited by a moderator: Mar 20, 2008
  2. jcsd
  3. Mar 20, 2008 #2


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    Staff: Mentor

    1. Why?
    2. Don't think that's right
  4. Mar 20, 2008 #3
    1. Beacuse dont the sum of the torques have to be zero?
    2. Oh its torque isnt it?
    are the others ok?
  5. Mar 20, 2008 #4


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    Staff: Mentor

    You have the right answer to my "Why?" question. Do you have the right answer to their question? Watch out for negatives like "not" and "never" in questions....

    The only other one I checked was #7, and at first glance it doesn't look right. Aren't they asking where to place a larger mass to balance out the first one? If the 2nd mass is larger, and you want the sum of the torques to be zero, do you place the heavier mass farther out or closer in?
  6. Mar 20, 2008 #5
    Does anyone else know if my other answers are correct?
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