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Homework Help: Time for a bomb to hit the ground

  1. Feb 23, 2008 #1
    1. The problem statement, all variables and given/known data
    Bush fir patrols sometimes drop small bomb to start a controlled burn off from aeroplanes. Peter was flying his over a forest at constant horizontal speed of 75m/s and at contsant altitude of 490m when he dropped the bomb.
    A) how long does it take for the bomb to hit the ground?

    2. Relevant equations
    we have a displacement (490m) , an acceleration (gravity, 9.8 m/s/s) and a velocity (75m/s), so v = u + at could be transposed to give time, however im hopeless at this. please advise..
    3. The attempt at a solution
    after some fiddling around with other formulae such as t = s/v = 6.53 s.. which according to the answers section is wrong.. they say 10s.. is this right? please advise me on this ASAP please..
  2. jcsd
  3. Feb 23, 2008 #2
    Welcome To PF.

    When the bomb is dropped from the aeroplane it has some horizontal velocity which is equal to the velocity of the aeroplane i.e. 75 m/s.
    Use concepts of horizontal and vertical components of velocity.Use accln along x axis=0 and accln along y-axis = g.Use s[y]: 490 m.

    Now use simple kinematic equations.

    suggestion= the simple basic formulae are very important but in these kinda questions they will not be aplicable becoz as there are horizontal and vertical components of velocityand accln involved.
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