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Finding the speed of a car

  1. Aug 29, 2015 #1
    1. The problem statement, all variables and given/known data

    There is one car which got stolen which goes from the point 30 in the negative sense of the "x" axe towards the point 0 and has a constant speed of 160 km/h. Another person notices the stealing 3 minutes later and takes another car to catch the stealer. What must be the minimal speed fo the car to catch the stealer before he reacher the point 0 ? (This is all one dimension, btw)

    2. Relevant equations

    average speed on x = delta x / delta t

    3. The attempt at a solution

    I found the following two equations :
    -160= (x -22)/t (The stealer reaches the point 22 3 minutes later)

    Vx= (x-30)/t (The guy who notices he got stealer)

    I don't know what to do at this point :/ A hint would be good. Thank you
  2. jcsd
  3. Aug 30, 2015 #2


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    Science Advisor

    You need to include the units.
    There is km/hr and minutes involved so some conversion is necessary.
    It's unclear what significance you think 'point 22' has, it's not important where the first car is when the second car starts. All that matters is that they both reach x=0 at the same time.

    The first car starts 30km from the origin, how long does it take to travel 30km at 160km/hr? (v & d known, t unknown)
    How fast must the second car go to cover that same distance in 3 minutes less time and meet the first car at x=0? (t & d known, v unknown)
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