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Finding the Spring Constant of a ball

  1. Oct 22, 2008 #1
    1. A spring clamped to a table shoots a 20 g ball horizontally. When the spring is compressed 18 cm the ball travels horizontally 5.1 m and lands on the floor 1.7 m below the point at which it left the spring. What is the spring constant (in N/m)

    2. I tried using k=mg/x (x being distance of the spring compression) but am at a COMPLETE loss as how to solve it!
  2. jcsd
  3. Oct 22, 2008 #2


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    Homework Helper

    Welcome to PF.

    This is a double problem.

    First find the initial velocity, which is totally in the x direction.

    You do that by figuring the time for it to drop 1.7 m.

    Take that time and determine horizontal velocity by 5.1 m / Time to drop.

    Now for part 2:
    You know the V so you know KE which is mV2/2

    If you know KE then you know how much PE was initrially in the spring by PE = k*x2/2

    You know x, you know PE now you can finally know k.
  4. Nov 12, 2008 #3
    i have a similar problem to this one and am stuck. Isn't the ball moving in the y direction also since it falls below where it left the spring?
  5. Nov 12, 2008 #4


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    Homework Helper

    Welcome to PF.

    Yes. Gravity does develop a y component of velocity. But the x component only is the initial velocity and it is this velocity that determines how far from the table it lands.

    The Vx * t is that distance. Hence the importance of calculating the t in order to determine that distance.
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