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Homework Help: Projectile Motion home work

  1. Mar 5, 2014 #1
    1. The problem statement, all variables and given/known data
    A projectile launched straight up at 10 m/s will be in the air for:

    A) 1 s

    B) 1.4 s

    C) 2 s

    D) 5 s

    2. Relevant equations
    Not sure.

    3. The attempt at a solution

    I'm honestly not sure what to make of this problem. Since it's freefall, it sounds like we could assume the acceleration to be -10 m/s2. V0 would be equal to 10 m/s and V would equal 0 if it reaches a maximum height. If we need to find t and since we aren't given d, can we use the equation:

    v = v0+at?
  2. jcsd
  3. Mar 5, 2014 #2
    There are a couple ways for this problem. That equation will work to find the time it takes to reach its maximum height, but keep in mind that the time in the air will be the time it takes to reach that height and then return to the starting height. Since the path is symmetric (i.e. same motion up and down), how does that time compare to the total time?
  4. Mar 5, 2014 #3
    If the equation in my first post will help to find the total amount of time that it takes for the ball to complete the height, then would we need to find half the amount of time it would take for the ball to reach maximum height and then double that time to find the total time to reach the point (both in reaching max height and falling back down). Is that right?
  5. Mar 6, 2014 #4


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    Gold Member

    I don't quite understand what you said.

    The equation finds the time taken for the projectile to come to rest.As we know,the projectile will come to rest at maximum height and again start fall down.
    So now we know the time taken to reach maximum height.Can you find the time taken to fall down?
    There are two ways.
  6. Mar 6, 2014 #5
    Time of Flight = 2u(sinΘ)/g

    Also what is implied when an object is projected and returns to it's starting position wrt to displacement...you can also form an equation with this involving time
    Last edited: Mar 6, 2014
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