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Homework Help: Kinmatics easy problem

  1. Jul 10, 2004 #1
    Hi there,
    Please help me with this problem
    I read physics on my own so this is not a homework !!

    Suppose you fire a rifle bullet (1600 m/s) in a shooting gallery and hear the gong on the target ring 0.731 s later.
    Taking the speed of sound to be 330 m/s and assuming the bullet travels straight downrange at a constant speed, how far away is the target ?

    Here is my work :
    Given { (v_1) = 1600 m/s, (v_2) = 330 m/s, t_T = 0.731 }
    Find {l}
    There is a distance between us and the target ring (l) that the problem asks to find it.
    I know that when speed is constant or we know the average speed we can find (l) the distance traveled :
    l = t.v
    But in the problem we don’t have t_1 ( the time taken by bullet to reach the target ) and we don't have t_2 ( the time taken by sound to reach our ear ) then we must have v_T (The average speed in from firing the bullet till reaching the sound to our ears ) but to finding that we need to know l_T ( the total distance traveled ) so what shall we do ?

  2. jcsd
  3. Jul 10, 2004 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Welcome to PF! Don't be afraid to ask questions, as long as you show your work.

    Write down what you do know. Start with t_1. Since d = vt, we have:
    (1) [itex]L = v_{bullet}t_1[/itex]
    And then for t_2, we have:
    (2) [itex]L = v_{sound}t_2[/itex]
    But we know t_T = t_1 + t_2, so can you find an equation for t_T in terms of the speeds and distance?
  4. Jul 10, 2004 #3
    Yes I can !
    With PF I don't feel lonely in the rest of the way in studying physics.
    Thank you very much.
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