Ask Experts Questions for FREE Help !
Ask
    solidsnake11's Avatar
    solidsnake11 Posts: 4, Reputation: 1
    New Member
     
    #1

    Mar 20, 2011, 02:30 PM
    Equilibrium Rules Physics Question - Help please
    A crane is used to raise one end of a 15kN girder of length 10m off the ground. When the end of the girder is at rest 6m off the ground, the crane cable is perpendicular to the girder.

    a) calculate the tension in the cable

    b) Show that the support force on the girder from the ground has a horizontal component of 3.6N and a vertical component of 10.2kN.

    I'm really stuck guys - any help would be greatly appreciated.

    Thanks
    jcaron2's Avatar
    jcaron2 Posts: 986, Reputation: 204
    Senior Member
     
    #2

    Mar 21, 2011, 07:56 AM
    A) The cable is supplying enough tension to balance out the torque from gravity pulling on the girder around the axis of rotation where the girder is in contact with the ground. So what's the torque pulling the girder back to the ground? You can calculate it by assuming the entire weight of the girder is pulling straight down at its center. The center of the girder is 3m off the ground (vertical distance), 5m from the end of the girder in contact with the ground (this is the hypotenuse of a 3-4-5 right triangle), so the horizontal distance from the beam center to the end is 4m. Thus the torque on the beam is 15 kN * 4m = 60 kN*m. Meanwhile, the torque applied by the cable is T * 10m (where T is the tension) in the opposite direction. We know the moment arm is exactly 10m (the length of the girder) because the problem stated outright that the cable is perpendicular to the length of the girder.

    So since the torques have to be equal and opposite (so that the entire girder is static), we can say

    T * 10m = 60 kN*m
    T = 6 kN

    B) You now know both the magnitude and direction of the force applied by the cable (along with the force applied by gravity). If you simply sum up the horizontal and vertical components of those known forces, you'll find that the remaining support forces from the ground are exactly as the problem states.

Not your question? Ask your question View similar questions

 

Question Tools Search this Question
Search this Question:

Advanced Search

Add your answer here.


Check out some similar questions!

Physics equilibrium and statics problem [ 3 Answers ]

A uniform steel girder of weight 22kN and length 14m is lifted off the ground at one end by a crane. When the raised end is 2m above the ground, the cable is vertical. Calculate 1) the tension in the cable at this position and 2) the force of the girder on the ground. Any help would be...

Physics Question [ 1 Answers ]

Describe what is required for a magnetic field to be used to generate energy. How must a conductor loop be oriented and what must it do relative to the magnetic field. Thanks already!

Physics question [ 2 Answers ]

Two blocks attached by a string (see figure) slide down a 20° incline. Block 1 has mass m1 = 0.78 kg and block 2 has mass m2 = 0.23 kg. In addition, the kinetic coefficients of friction between the blocks and the incline are 0.30 for block 1 and 0.20 for block 2. (a) Find the magnitude of the...

Physics question [ 2 Answers ]

help me solve these problems: 1)A particle is exicuting SHM with time T .Starting from mean position ,what is the time taken by it to complete 5/8 oscillations ? 2)Two particles executing shm of same frequency meet at x= A/2 ,while moving in opposite directions . What is the phase difference...


View more questions Search