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Homework Help: Struggling with horizontal motion

  1. May 9, 2012 #1
    I'm currently studying Edexcel AS Physics (a UK-based examboard), I'm comfortable with problems where there is no horizontal component (so when something is thrown/released in a straight line; e.g. a ball thrown upwards), but I really struggle with problems that include the horizontal direction. I know that air resistance is neglected and thus the object will move with a constant velocity but it still doesn't make sense. For example, the below question:

    I usually use the UVATS/SUVATS method, but I am unsure what he values of these are in this case?

    u = is it 31 m/s ?
    v = ?
    a = (do we consider this)
    t = ?
    s = (not sure?)
  2. jcsd
  3. May 9, 2012 #2


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    Staff: Mentor

    Since you know that the horizontal and vertical components of the velocity are independent of each other, start by listing the known parameters of each. For example, what is the initial velocity in the horizontal direction? How about the vertical direction?

    If you consider the horizontal motion alone, how long does it take to complete the portion of its journey that is of interest?
  4. May 10, 2012 #3
    I think I got it:


    u = 31 m/s
    s = 2.7 m

    since s = ut
    s/u = t = 2.7/31 = 0.0870 seconds


    u = 0 m/s
    t= 0.0870 s
    a= 9.8 m/s2
    s = s

    s = 0.5(9.8)(0.0870)2
    s = 0.0371 m
    s= 3.71 cm

    The time a projectile is in flight, is always the same when considering vertical and horizontal right?

  5. May 10, 2012 #4


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    Staff: Mentor

    Yes, your method and results look good. Nicely done.
    Right. It couldn't be otherwise unless the projectile could be in two places at once!
  6. May 10, 2012 #5
    Ahh yes! Thanks :)
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