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Homework Help: Higher physics - rearranging prob

  1. Aug 5, 2008 #1
    1. The problem statement, all variables and given/known data

    A nail is fired from a nail gun into a fixed block of wood. The nail has a speed of 380 m s-1 just as it enters the wood.

    The nail comes to rest after penetrating 60 mm into the wood.

    Find the time taken for the nail to come to rest. Assume that the retarding force on the nail is constant as it penetrates the wood.

    http://www.bbc.co.uk/scotland/education/bitesize/higher/img/physics/mech_matt/analyse_motion/example1.gif [Broken]

    2. Relevant equations
    u = 380 m s-1
    v = 0
    a = ?
    t = ?
    s = 60 x 10-3 m

    3. The attempt at a solution

    v2 = u2 + 2as
    02 = 3802 + 2a x 60 x 10-3
    a = -120333 m s-2

    This was from a revision site so they gave the answer, however my problem is that I'm unsure on how to re-arrange the formula properly.

    Having just started higher physics (scotland) this doesnt bode too well.
    Last edited by a moderator: May 3, 2017
  2. jcsd
  3. Aug 5, 2008 #2
    HINT: Use another equation of motion, now that you have a value for a.
  4. Aug 5, 2008 #3
    v = u +at
    0= 380 + (-120333)t
    t = 0.0003157

    Is the answer given, I'm just having trouble getting my head around the re-arranging of formulae :/
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