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Homework Help: Energy and WET (Springs)

  1. Oct 17, 2008 #1
    A toy cannon uses a spring to project a 5.30 g soft rubber ball. The spring is originally compressed by 5.00 cm and has a force constant of 9.00 N/m. When it is fired, the ball moves 16.0 cm through the horizontal barrel of the cannon, and a constant frictional force of 0.0320 N exists between barrel and ball.

    (a) With what speed does the projectile leave the barrel of the cannon?

    Wnet = [tex]\Delta[/tex]KE
    Ws - Wfk = .5mv2 - 0
    .5kx2 - fkd = .5mv2
    .5(9)(.052) - (.032)(.11) = .5(.0053)v2
    v = 1.7079

    Final answer is incorrect. Any ideas?
  2. jcsd
  3. Oct 17, 2008 #2
    Have you tried replacing .11 with .16? Friction acts over full length of barrel. What is the answer?
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