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Homework Help: Equations on Newton1 and 2

  1. Sep 20, 2011 #1
    1. The problem statement, all variables and given/known data

    A student pulls two trolleys, which are connected by a piece of string. the mass of the string is negligible. there is a horizontal force of 12N

    Trolley1: 1kg
    Trolley 2: 3kg

    1. Calculate acceleration of the trolley.
    2. determine the force exerted by the connecting string on each trolley.

    2. Relevant equations

    3. The attempt at a solution

    1. F(res)=ma F(g)=mg
    F(g) - F(A)= ma =(4)(9,8)
    39.4 - 12= 4a =39,2
    a= 6,85m/s^2

    2. Trolley1: F(res)=ma F(g)= mg
    F(T)-F(g)=ma = (1)(9,8)
    F(T) - 9,8= 6,85 =9,8
    F(T)= 16,65N

    Trolley2: F(res)= ma F(g)= mg
    F(T)- F(g)= ma =(3)(9,8)
    F(T) - 29,4) = (3)(6,85) =29,4
    F(T)= 49,95N
  2. jcsd
  3. Sep 20, 2011 #2


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    Gold Member

    You need to separate out the x and y directions. The applied force of 12 N is horizontal. Look at the force in the x direction (horizontal direction) acting on the system, and use F_net in x direction = ma to solve for the acceleration in the x direction. Don't add F(g) forces to it, since those act in the y direction.

    Calculate the tension in the string connecting the trolleys by drawing a free body diagram of the last trolley, identifying the forces, and using Newton 2 again on that body.

    Check your work by drawing a FBD of the first trolley and proceeding in the same manner.
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