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Velocity Problems

  1. Oct 8, 2007 #1
    1. The problem statement, all variables and given/known data
    An auto travels at the rate of 25 km/hr North for 4 hours, then at 50 km/hr North for 8 hours, and finally 20 km/hr North for 2 hours. Find (a) the total distance covered in km and (b) the average velocity for the complete trip in m/s.


    2. Relevant equations
    d=vt


    3. The attempt at a solution
    >
    v1= 25 km/hr N
    t = 4 hrs
    >
    d=vt
    d1=(25km/hrN)(.......)
    If someone can just work through this and tell me what things mean and why that would be great.


    4. Answer from Teacher
    540 km; 107(or 10.7) m/s N


    1. The problem statement, all variables and given/known data
    A train travels at an average velocity of 120 km/h for 3 hours, then at 80 km/h for 210 km. The train stop for 1 hour. Finally, the train covers 300 km in 2.9 hours. All motion is to the NORTH. (a) What is the train's displacement at the end of the first 3 hours? (b) How much time was spent going 80 km/h in the second leg of the trip? (c) What was the average velocity for the final 3.9 hours of the trip? (d) Calculate the average velocity for the whole trip. (e) Calculate the average velocity if the second part of the trip (80 km/h for 210 km) were to the SOUTH.


    2. Relevant equations
    d=vt


    3. The attempt at a solution
    Honestly, with this question I have no clue what to do. Same as above, if someone can help me go through this that would be great.


    4. Answer from Teacher
    360 km N; 2.6 hr; 103.4 km/hr N; 91.6 km/hr W; 47.4 km/hr N
     
    Last edited: Oct 8, 2007
  2. jcsd
  3. Oct 8, 2007 #2
    For part A:

    Break it down,

    25 km/hr North for 4 hours = 100km for 4 hours
    50 km/hr North for 8 hours = 400km for 8 hours
    20 km/hr North for 2 hours = 40km for 2 hours

    Total km = 540km

    Do you understand what I did there?
     
  4. Oct 8, 2007 #3
    I do but my teacher wants me to do it in equations, like how I wrote in the attempt at solution, v1 = ..... , t = ....... and etc. When I do this I get confused of what to multiply by and etc. Also with directions, like E, N and etc, do these change the problems drastically or very little? How too.
     
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