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Physics HW

  1. May 18, 2005 #1
    1. If the torque required to loosen a nut is 40.0 mN, what miminum force must be exerted by a mechanic to the end of a 30.0 cm wrench to remove the nut?

    2. A uniform bridge 20.0 m long and weighting 4.00 x 10^5 N is supported by pillars located 3.00 m from each end. if a 1.96 x 10^4 N car is parked 8.00 m from one end of the bridge, how much force does each pillar exert.

    3. A person lifts a 950 N box by pushing it up a incline. If the person exerts a force of 350 N along the incline, what is the mechanical advantage of the incline?

    4. A 35 kg bowling ball with a radius of 13 cm starts from rest at the top of an incline 3.5 m in height. Find the translational speed of the bowling ball after it has rolled to the bottom of the incline. (Assume the ball is a uniform solid sphere.)
     
  2. jcsd
  3. May 18, 2005 #2

    Pengwuino

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    Gold Member

    This is in the wrong section and you need to show us the work you've done so far.
     
  4. May 18, 2005 #3
    the following four questions were from my test that i recentally took and i miss the day that we went over them and didn;t get the answers and haven;t had to time to check with my teacher about them, so i need some help on what the answers would be. thanks.

    1. If the torque required to loosen a nut is 40.0 mN, what miminum force must be exerted by a mechanic to the end of a 30.0 cm wrench to remove the nut?

    2. A uniform bridge 20.0 m long and weighting 4.00 x 10^5 N is supported by pillars located 3.00 m from each end. if a 1.96 x 10^4 N car is parked 8.00 m from one end of the bridge, how much force does each pillar exert.

    3. A person lifts a 950 N box by pushing it up a incline. If the person exerts a force of 350 N along the incline, what is the mechanical advantage of the incline?

    4. A 35 kg bowling ball with a radius of 13 cm starts from rest at the top of an incline 3.5 m in height. Find the translational speed of the bowling ball after it has rolled to the bottom of the incline. (Assume the ball is a uniform solid sphere.)
     
  5. May 18, 2005 #4

    Pengwuino

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    Don't you have a book?
     
  6. May 18, 2005 #5
    no forgot it at school but brought folder home, for #1 i get 133.3 N, #2 i don't know how to get N_1 and N_2, #3 i was told to do 950/350 but i believe he is just looking for a word answer, and #4 i get to the end but i don't know how to solve for vf^2.
     
  7. May 18, 2005 #6
    Step One, write down everything you know:

    Bridge length =[itex] L = 20m[/itex]
    Bridge weight = [tex] m_{bridge}g = 4 x 10^5N[/itex]
    Car weight = [tex] m_{car}g = 1.96 x 10^4N[/itex]
    Car distance = [itex] d = 8m[/itex]
    Pillars = [itex] P_1\ and \ P_2 = 3m \ and\ 17m[/itex]

    Step Two, Identify your unknowns:

    Force on both pillars due to the bridge and car.

    Step Three, Formulate a set of equations that describe the problem:

    The system is in equilibrium since nothing is moving. This means the net force at any point is zero. The net torque at any point is also zero. There are two axes of rotation, the two pillars. We will pick the left pillar [itex] P_1[/itex] as our zero point:

    [tex] F_{net} = T_{net} = 0 [/tex]

    The system exerts torque on both pillars. Find the center of mass of the system (bridge and man) and find the torque that this CM applies on both pillars.

    [tex] \tau_{net} = \tau(P_1) + \tau(P2) = (CM_{system})(CM_{dist}) [/tex]

    Step Four , Solve the equations for your unknown:

    Step Five , Plug in your numbers and get an answer:

    Step Six , Answer the question:


    Can you finish the last 4 steps?
     
    Last edited: May 18, 2005
  8. May 18, 2005 #7
  9. May 18, 2005 #8
    i am still lost even with the help of the other post. i don;t know where cm's come from and how to get them.
     
  10. May 18, 2005 #9
    was my answer to #1 correct???
     
  11. May 19, 2005 #10
    #1 The torque required is 40mN, your answer would be correct if the torque required was 40N. Remember the prefix 'm' means milli, or 10^-3
     
  12. May 19, 2005 #11
    Is that enough for #3? For #2, You must have been taught how to find center of masses before dealing with problems like this.
     
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