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HELP i dont no how to do this problem

  1. Apr 29, 2007 #1
    Problem:
    A flare was fired straight up at a speed of 25 m/s from the bed of a truck traveling along a level road at a speed of 15 m/s.

    a. Assuming the flare landed back in the bed of the truck, how much time was the flare in the air?

    b. How far horizontally did the flare travel before landing back in the bed of the truck?

    c. What maximum height did the flare reach?



    Some equations that i thought might help with this problem are
    deltaX=vi+deltaT*1/2adeltaT^2
    but since i do not no the cange in X or the time i can not use this equation



    To try and figure out this problem i made a chart showing what horizontal and vertical things that i already knew


    H V
    0=ax ay=10 m/s^2 ​
    15 m/s=Vxi Vyi=25 m/s​
    =deltaX deltaXy=​
    deltaT=​
     
    Last edited: Apr 29, 2007
  2. jcsd
  3. Apr 29, 2007 #2
    You could do this by considering energy. There are a number of ways to do it. As I read it you have plenty of information here to do it with.
     
  4. Apr 29, 2007 #3
    how would i use energy to solve a problem on projectiles?
     
  5. Apr 29, 2007 #4
    because i havent learned how to use energy in problems like this i would need some guidance or a different way to solve the problem that is more commonly used for motion projectile problems
     
  6. Apr 29, 2007 #5

    Mentz114

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    Gold Member

    You can work out how long the flare was in the air, and high it goes, just from its initial vertical velocity. If the flare has mass m then the initial kinetic energy is 1/2mv^2, v= 25 m/s. When it turns around and strats falling it has potential energy mgh. Set these equal and you can work out h. Remember that the flare travels horizontally at the same speed as the truck.
     
  7. Apr 29, 2007 #6

    Mentz114

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    Gold Member

    You've posted the same question in two forums. That is against the rules. Next time I'll report you.
     
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