1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The law of the machine

  1. Jun 21, 2008 #1
    1. The problem statement, all variables and given/known data

    A screw jack has a single start thread of pitch 7mm and a operating handle 800mm long.when raising a load of 750kg the effort required on thev end of the handle is 26N.
    determine for these operating conditions the following :
    (a) the mechanical advantage
    (b) the velocity ratio
    (c) the efficiency of the machine
    (d) the law of the machine

    2. Relevant equations
    ma = load/effort
    vr = 2 x pie x r/p
    effiency of the machine = ma/vr x 100%
    law of the machine = E = aw+b


    3. The attempt at a solution

    (a) mechanical advantage = 750 x 9.81/26N = 282.98

    (b) the velocity ratio = 2 x pie x 800mm/7mm = 718.07

    (c) the effiency of the machine = 282.98/718.07 x 100% = 39.40%

    (d) the law of the machine this is where i am struggling i no the formula is E = aw+b

    where a is the velocity ratio and w is the load however what does the b stand for and if i need to caculate this how do i do this please help ......
     
  2. jcsd
  3. Jun 21, 2008 #2
    Substitute the values of E,a,w in the law of machines to obtain the value of b (it is a constant).
     
  4. Jun 21, 2008 #3
    so i have transposed correctly i think and have came up with this :


    b = E-a/w

    therefore b = 26n - 718.07/750 x 9.81 = 16.60

    thanks for the quick reply
     
  5. Jun 21, 2008 #4
    sorry to reply again as i have misread part (e) in the question

    it says if the effort needed to raise a load of 400kg is 17N determine :

    the law of the machine.

    also should the law of the machine when calculated total 17N

    thanks again mark
     
  6. Jun 22, 2008 #5
    I don't understand what you mean by this.


    However, you have been provided with two sets of values for E and W. Substitute these in the law of machines, and obtain the values of 'a' and 'b' by solving the system of linear equations that you get.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: The law of the machine
  1. Gravitational machines (Replies: 16)

  2. DC Machines (Replies: 1)

  3. Electrical machines (Replies: 0)

  4. Induction Machine (Replies: 3)

Loading...