1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Elastic Potential Energy and the Spring Constant

  1. Oct 6, 2006 #1
    1) A 60 kg person drops from rest a distance of 1.20 m to a platform of negligible mass supported by a stiff spring. The platform drops 6 cm before the person comes to rest. What is the spring constant of spring?

    a.4.12E5-------b. 2.56E5---------c. 3.92E5--------d. 5.45E4----e. 8.83E4

    I don’t know if I did this setup correctly, but I got c. as my answer. Please tell me if my equations are incorrect or if I neglected another energy quantity.

    U2 = U1

    Mgh2 + (k*x_2^2)/2 = mgh1 + (k*x_1^2)/2
    (k*x_2^2)/2 = mgh1

    k = (2mgh)/(x^2) = (2*9.80 m/s^2*1.20 m)/(0.06 m)^2 = 392000 N/m

    2) A spring-loaded dart gun is used to shoot a dart straight up into the air, and the dart reaches a maximum height of 24 m. The same dart is shot up a second time from the same gun, but this time the spring is compressed only half as far (compared to first hot). How far up does dart go this time (neglect friction and assume spring obeys Hooke’s law)?

    a.48 m---------b. 12 m---------c. 6 m------------d. 3m

    I followed the same format as in #1, so, if that is wrong, this would be, too.

    (k*x_2^2)/2 = mgh

    at 24 m, h = (k*x^2)/(2mg) = 24 m

    when x = x/2, h = (k*x^2)/(4*2 mg) = (1/4)* (k*x^2)/(2mg) = (1/4)(24 m) = 6 m ???

  2. jcsd
  3. Oct 6, 2006 #2


    User Avatar
    Homework Helper

    Looks good to me, I hope I'm not missing something.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Elastic Potential Energy and the Spring Constant