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!

Work done and energy transfer

  1. Aug 4, 2015 #1
    1. The problem statement, all variables and given/known data
    image.jpg

    2. Relevant equations
    KE = 1/2mv^2
    f = -kx
    U = 1/2kx^2
    Kinematic equations
    F = ma

    3. The attempt at a solution
    Horizontal components of the block's weight: 8.38N

    Compression of the spring:
    f = -kx
    8.37 = -500x
    x = 0.01674 m , which is wrong and I would be grateful if someone can explain to me why it is wrong

    Then, I changed the approach

    Find the acceleration of the block

    F= ma
    8.37 = 2.5a
    a = 3.348 ms^-2

    u = 0.75, v = ?, a = 3.348, s = 0.3

    v^2 = u^2 + 2as
    v^2 = 0.75^2 + 2(3.348)(0.3)
    v = 1.603 m/s

    W = KE change when the blocj hit the spring
    W = 1/2(2.5)(1.603)^2 - 1/2(2.5)(0)^2
    W = 3.212J

    Since work done can also be treated as potential energy

    U = 1/2kx^2
    3.212 = 1/2(500)x^2
    x = 0.113 m

    and is still wrong, why???

    Thanks!
     
    Last edited: Aug 4, 2015
  2. jcsd
  3. Aug 4, 2015 #2

    DEvens

    User Avatar
    Education Advisor
    Gold Member

    The block is trading potential energy from height for kinetic energy. Then it hits the spring. It starts trading kinetic energy for spring energy.

    When does the block stop? When its kinetic energy reaches zero. That happens when the compression energy of the spring equals the potential energy the block has lost by sliding down the ramp.

    Don't forget the block is still sliding down after it contacts the spring, so it still loses height until it stops.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Work done and energy transfer
  1. Energy and Work Done (Replies: 5)

Loading...