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Homework Help: Spring force and frictionless mass vs speed

  1. Oct 18, 2014 #1
    1. The problem statement, all variables and given/known data
    A mass
    (m = 1.35 kg),
    originally at rest, sits on a frictionless surface. It is attached to one end of an unstretched spring
    (k = 747 N/m),
    the other end of which is fixed to a wall (see figure below). The mass is then pushed with a constant force to stretch the spring. As a result, the system (which consists of the wall, spring and mass) comes to a momentary stop after the mass moves 15.0 cm. Find the following.

    (e) speed of the mass 4.50 cm into the motion

    2. Relevant equations

    3. The attempt at a solution
    I tried 1/2mv^2 = 1/2K (x1^2-x2^2)
    v= sqrt(K ( (0.15^2-0.045^2))/m

    not sure how to solve this .. been at it for a while now.

    Attached Files:

  2. jcsd
  3. Oct 18, 2014 #2


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    I haven't tried to solve it but... when the mass comes to a momentary halt you know all the applied energy is stored in the spring.
  4. Oct 18, 2014 #3


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    Hello wind, and welcome to PF.

    Your attempt is based on an equation for energy conservation.
    You might need another term. How about something that features F ?
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