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Two blocks, one is hanging

  1. Jul 2, 2008 #1
    Whoops, I know i made another post but i didnt realize i have another question that i left blank:


    The weight of the block on a table is 452 N and that of the hanging block is 220 N. Ignore all frictional effects, and assuming the pulley to be massless.


    What is Acceleration of the two blocks?

    What is the tension?
     
  2. jcsd
  3. Jul 2, 2008 #2
    So what i did was i tried to isolate the two Ns and i got seperate masses.

    Then i did this: (452-220)/(46.1+22.4)

    but that was wrong.
     
  4. Jul 2, 2008 #3

    rock.freak667

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    Assuming downward motion.

    What is the resultant downward force on the hanging block?

    and what would be the resultant force on the block on the table?
     
  5. Jul 2, 2008 #4


    Is the force in the downward position simply 220 N?
     
  6. Jul 2, 2008 #5

    rock.freak667

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    There is tension,T, in the string acting upward. So the resultant downward force = (220-T)N

    and if that block moves down, how does the other block move and what would be the resultant force on it?
     
  7. Jul 2, 2008 #6
    if one block moves down the other moves to the left. the acceleration has to be the same since its a closed system. So the downward force is ma=220-T? what is "m"?
     
  8. Jul 2, 2008 #7

    rock.freak667

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    Yes

    Correct

    m is the mass of the 220N block. Depending on what you take 'g'. (W=mg)
     
  9. Jul 2, 2008 #8


    Ok. So now what?

    22.4a=220-T?

    I dont know a or T
     
  10. Jul 2, 2008 #9

    rock.freak667

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    The other block moves to the left making Ma=T (where M is the mass of the 452N block)
     
  11. Jul 2, 2008 #10
    So the correct equation is 22.4a=220-(ma of the other block)?

    I'm getting so confused.
     
  12. Jul 2, 2008 #11
    Ok os i reworked the problem and i got 3.39 as the acceleration is this correct?
     
  13. Jul 2, 2008 #12

    rock.freak667

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    Take one block at a time.

    We know for the hanging one it's 22.4a=220-T


    Now since the one on the table moves to the left and the only force on it is the tension,T, then the resultant force is Ma=T where M=mass of the 452N block.

    solving them will give

    22.4a=220-Ma

    22.4a+Ma=220. Find a.
     
  14. Jul 2, 2008 #13

    rock.freak667

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    It is somewhere around 3, I got 3.21 using g=9.81 but I kinda did it in my head so it might be a bit off.
     
  15. Jul 2, 2008 #14
    so the tension in the cord is simply the accelration of the system times the mass of the 452 N block?
     
  16. Jul 2, 2008 #15
    3.39 was incorrect. I have 10 minutes left to submit this and no luck whatsoever :(
     
  17. Jul 2, 2008 #16
    3.21 was correct, now the tension: T=mass of the 452 block * 3.21?
     
  18. Jul 2, 2008 #17

    rock.freak667

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    Yep.
     
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