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Homework Help: Final velocity help

  1. May 19, 2015 #1
    What will the final velocity of 5.0 g bullet starting from rest if a net force of 45 N is applied over a distance of 0.80 m ?


    3. i tried to solve it but i don't know of my anwer is correct
    F=ma, F/m=a
    45/.005 kg
    From this formula ( d=1/2at^2) we can say that
    Time= 2d/a and then take under root
    2×0.80/9000 (under root or square root)
    =0.013 sec
    initial velocity (u) =0
    answer is 117m/s^-1
    Last edited by a moderator: May 19, 2015
  2. jcsd
  3. May 19, 2015 #2
  4. May 19, 2015 #3


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    You get 120m/s if you don't round down to 0.013 seconds.
  5. May 19, 2015 #4
    I don't understand what you mean by this. Please tell what does it mean because i am only in 8 grade
  6. May 19, 2015 #5
    What CWatters means is that 0,013 s is not the exact value of the time. If you use the exact value, which is t = (2*0,8/9000)^(1/2), you will get a slightly different, more correct answer. I would recommend googleing "significat numbers". :)
  7. May 19, 2015 #6
    Thank you very much for your help. I also had the same answer but the problem was that i shortened 0.0133333333333 to 0.013 thats why my answer was 117 and not 120.
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