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Find its maximum height and initial velocity

  1. Oct 3, 2004 #1
    Hello i have been able to do 7 out of 8 question on my linear motion questions, but this last question number 8, is proving difficult. I don't know whether the tutor has made a mistake (as the answers are typed at the bottom) so if you could be of help i would be very glad ty.

    I am using s = u.t + 0.5.a.t^2

    and v = U + a.t

    but neither bring up the correct answers:

    8. A pistol pellet is fired vertically upwards and lands back at its firing point
    8 seconds later. Neglecting air resistance, and assuming the acceleration due to gravity is g = 9.81 m/s2 downwards ! find its maximum height and initial velocity.
    [answers: 78.5 m , 39.2 m/s]

    Ty every so much :-)
  2. jcsd
  3. Oct 3, 2004 #2
    Welcome to PF :biggrin:
    The bullet starts with velocity v,slows down due to gravity,and attains v=0 at max height.Then it picks up speed(due to gravity) and reaches down with total velocity v.
    So time taken to attain v=0 is 8/2=4s.
    I plugged this into the eqn and got the given answer.
    Similarly,height reached is when velocity becomes 0,I got the given answer with the eqn you gave.
    I think you tried t=8s.I hope you understood.
    Last edited: Oct 3, 2004
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