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Homework Help: Newton's laws

  1. Aug 11, 2009 #1
    1. The problem statement, all variables and given/known data

    A force F applied to a mass m1 produces an acceleration of 3.0 m/s2. The same
    force applied to a second object of mass m2 produces an acceleration of 1.0

    a. Find the value of the ratio m1 / m2.
    b. If m1and m2 are combined, what will be the acceleration of the combined mass (m1+ m2) under the action of the force F?

    2. Relevant equations


    3. The attempt at a solution


    I didn't know where to begin. So I chose a random number and assumed that my force was 6 N.

    6N = m1 a1
    6N = m1 (3.0 m/s2)
    6N / 3.0 m/s2 = m1
    2 kg = m1

    6N = m2 a2
    6N = m1 (1.0 m/s2)
    6N / 1.0 m/s2 = m2
    6 kg = m2

    m1/m2 = 2kg/6kg = 0.333 = 3 x 10 -1


    F = (m1+m2) a
    6N = (2kg + 6kg) a
    6N / 8kg = a
    0.75 m/s2 = a


    Any suggestions? :)
  2. jcsd
  3. Aug 11, 2009 #2


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    Homework Helper

    While this is correct. You didn't need to say F=6. It said the it applied the same force so F1=F2
    or simply put m1a1=m2a2

    So if F is the same, either F=m1a1 or F=m2a2

    So you want F=(m1+m2)a . So you can put F equal to which either one you want and solve from there.
  4. Aug 12, 2009 #3
    Makes more sense! Thanks :)
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