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Homework Help: One dimensional motion

  1. Aug 26, 2012 #1
    1. A uniformly retarded moving motorcycle covers 250 meters in the first 10 seconds and and 250 meters in the next 20 seconds.How much will it travel more to come before coming to a halt?

    250 = 10u - 50a , 250 = 20u - 200a. On solving these i get and a retardation of 2.5.
  2. jcsd
  3. Aug 26, 2012 #2


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    Although it is hard to understand your work, which was not well explained, I get that you applied the equation d = ut + (1/2)at2 twice, once for each time period. This is the correct thing to do.

    Did you assume that 'u' was the same between both equations? Because it's not the same u. The u in your first equation is the initial velocity at the beginning of the 10 second period. The u in your second equation is the initial velocity at the beginning of the 20 second period. These are not the same, but you can *relate* them using the equation for speed vs time.
  4. Aug 26, 2012 #3
    An alternative method to the one above, that gives you two equations with the same u (initial velocity) would be to use the fact that you know how far the bike has traveled after 30 seconds :)
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