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Homework Help: Newton's second law (Probably a simple question)

  1. Feb 25, 2010 #1
    1. The problem statement, all variables and given/known data
    A car pulls a trailer along a level road at a steady speed of 10 m/s and the pull on the trailer is 100N. When the car accelerates at 0.5 m/s2 the pull on the trailer is 150N.
    Assuming the resistance to motion to be constant, find the mass of the trailer.

    2. Relevant equations

    3. The attempt at a solution

    My assumption is that since there is no acceleration in the first case, the pull on the trailer (100N) must be balanced by a resistive force (100N). Since the resistance to motion is said to be constant, in the latter case the resistance would still be 100N.

    The net force while accelerating would be 50N (150N - 100N), so using F = ma, mass should be found by dividing 50N by 0.5 m/s2.

    I've calculated the trailer's mass as 100kg.

    I feel uneasy about the question, it seemed fairly straight-forward, just wanting an outside opinion... have I calculated this correctly?
  2. jcsd
  3. Feb 25, 2010 #2
    Your calculation looks fine to me!
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