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Homework Help: Speed for Remaining Time and Distance

  1. Sep 19, 2010 #1

    MysticDude

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    Gold Member

    Hi people of PF! Okay so I just want you guys to check if my work is correct and if it not, help me fix it :D.

    1. The problem statement, all variables and given/known data
    You are to drive to an interview in another town, at a distance of 300km on an expressway. The interview is 11:15 AM. You plan to drive at 100 km/hr, so you leave at 8:00AM. to allow some extra time. You drive at that speed for the first 100 km, but then construction work forces you to slow to 40km/hr for 40 km. What would be the least speed needed for the rest of the trip to arrive in time for the interview?

    GIVEN
    Distance for travel is 300km
    First hour of travel was at 100km/hr
    Second hour of travel was at 40km/hr


    2. Relevant equations
    v = d/t where d is the distance and t is the time (1)
    d = v*t where v is the velocity (2)
    t = d/v (3)

    3. The attempt at a solution
    Okay so I figured that the total distance traveled is going to be 140km, meaning 160 km are left to travel. I also figured that 2 hours have been used to travel that time, meaning 1:15 hr are left. 1:15hr = 1.25hrs. So by using Equation (1) I get 160km/1.25hr = 128km/hr for the least amount of speed to get to the meeting at 11:15. I want to know if this answer is correct.


    Any help is greatly appreciated!
     
    Last edited: Sep 19, 2010
  2. jcsd
  3. Sep 19, 2010 #2

    MysticDude

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    Gold Member

    No more help needed, I just checked with an on-line tutor and I was correct.
     
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