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Kinematics - identifying and describing types of motion

  1. Mar 21, 2016 #1
    1. The problem statement, all variables and given/known data
    upload_2016-3-21_22-58-51.png

    2. Relevant equations
    average speed = total distance/total time
    average velocity = total displacement/total time

    3. The attempt at a solution
    please verify if my answers are correct. Thanks :D
    im specifically having doubts about a), i dont know how to identify when the truck moves at a quicker or slower pace. I've placed a star * beside phrases that i feel are incorrect. Please check them out.
    23.


    a)

    The truck *quickly moved 14.0 km (South) in 15 min. The truck continued another 6 km at a *slower pace over 10 min, and then stayed at this location for 5 min. The truck moved at a *slower pace and continued on for another 8 km towards the destination, taking 15 min for this portion of its journey.

    b)

    This motion represents non-uniform motion. This can easily be seen, since there are changes in the slope of the graph. This indicates that there are changes in the truck’s velocity and direction. As the truck picks up and delivers a cargo of cabbage, it will need to make turns on to other roads, change direction to take different routes, slow down at stop signs and traffic lights, and speed up to pass stop signs and traffic lights. In this case, the truck is not maintaining a constant velocity and is changing directions, so it is an example of non-uniform motion.

    c)

    total time = 25 min

    total displacement: d = 14.0 km + 6.0 km = 20 km

    average velocity = total displacement / total time

    average velocity = 20 km / 25 min

    average velocity = 0.8 km /min


    d)

    Total displacement = 8.0 km (S)

    t = 25 min

    Average velocity = total displacement / total time

    Average velocity = 8.0 km (S) / 25 min

    Average velocity = 0.32 km/min (S)
     
  2. jcsd
  3. Mar 21, 2016 #2

    haruspex

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    You might want to think about that again.
    Also, I suggest mentioning constant speed, where appropriate.
     
  4. Mar 21, 2016 #3

    Orodruin

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    a) You should not use non-quantified words such as "quick" and "slow". Quote the actual speed.

    b) You are here mostly describing a real truck, not the one in the graph, which only moves in one direction. Everything after "As the truck" is superfluous and not part of the solution.

    c) This is average speed, not average velocity. Please use correct terminology. You also have not distinguished what you call "total displacement" in c from what you call the same in d!
     
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