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Questions related to Kinematics

  1. Mar 22, 2016 #1
    • Member reminded that separate problems should be given separate threads.
    1. The problem statement, all variables and given/known data
    so im sending my unit in for marking, and i collected a bunch of kinematic related questions that i've attempted to answer, but dont know if im on the right track. Any help would be appreciated. Thanks.
    1.

    upload_2016-3-23_0-15-11.png
    2.
    upload_2016-3-23_0-16-50.png
    3.
    upload_2016-3-23_0-26-47.png
    upload_2016-3-23_0-27-5.png
    upload_2016-3-23_0-27-25.png

    4.
    upload_2016-3-23_0-35-1.png
    upload_2016-3-23_0-35-19.png
    5.
    upload_2016-3-23_0-36-30.png

    2. Relevant equations
    relevant equations are listed with each question

    3. The attempt at a solution

    1.
    The truck travelled 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 continued on at a constant speed for another 8 km towards the destination, taking 15 min for this portion of its journey.

    2.
    Displacement = 131 km (South)

    Average velocity = total displacement / total time

    Average velocity = 131 km (S) / 2.0 h

    Average velocity = 65.5 km /h (south)

    3.
    a)

    d = v x t

    Time to cross river:

    t = d / v

    = 0.032 km / 2.5 km/h

    = 0.0128 hrs

    Walking distance:

    d = (1.2 km/h) x (0.0128 hrs)

    d = 0.01536 km = 15.36 m

    Sandra will have to walk 15.36 m to reach the farmer’s market.

    b)
    Time it takes to cross the river:

    t = d / v

    t = 32.0 m (E) / 0.69 m/s (E)

    t = 46 s

    Time it takes to walk the riverbank:

    t = d / v

    t = 15.36 m / 0.72 m/s

    t = 21 s

    Walking to the farmer’s market will result in the shortest time for Sandra to reach her destination.

    4.
    Increase the launch angle above 45 degrees, to reduce the horizontal displacement. This way the water balloon will hit the target instead of passing it.

    5.
    is it because the supplies will be blown off course??
     

    Attached Files:

  2. jcsd
  3. Mar 23, 2016 #2

    andrewkirk

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    Are you sure it 'continued' in the same direction? What does the fact that the North-South coordinate is reducing over this 10 minutes tell us?
    Towards the destination? What do you mean by the destination? A place to deliver cabbages, or the home depot?
     
  4. Mar 23, 2016 #3

    haruspex

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  5. Mar 24, 2016 #4
    ok sorry about that :P
    "Are you sure it 'continued' in the same direction? What does the fact that the North-South coordinate is reducing over this 10 minutes tell us?"
    is the truck now travelling in an east-south direction?
     
  6. Mar 24, 2016 #5

    andrewkirk

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    We are given no information about its East-West coordinates. Only the North-South coordinates are given. Hence we should assume that it is travelling only along a road that runs North-South.
     
  7. Mar 24, 2016 #6
    so was the truck travelling North initially, but then began to travel towards the south direction?
     
  8. Mar 24, 2016 #7

    andrewkirk

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    No, travelling South first, because the coordinate given is the km to the South. THen turns and travels North later.
     
  9. Mar 24, 2016 #8

    haruspex

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    Nearly right. That might not be what you intended to say.
     
  10. Mar 24, 2016 #9
    so is this how it goes:
    The truck travelled 14.0 km (South) in 15 min. The truck then travelled another 6 km North at a slower pace over 10 min, staying at this location for 5 min. The truck continued on at a constant speed for another 8 km towards the destination, taking 15 min for this portion of its journey.

    also am i right that the truck continues at a constant speed?
     
  11. Mar 24, 2016 #10

    haruspex

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    Yes, but as has already been suggested you should state the speeds.
     
  12. Mar 24, 2016 #11
    oh ok, but im following the example in my lesson, so in that context do you think my answer is valid.
    upload_2016-3-24_20-12-28.png
    upload_2016-3-24_20-12-5.png
     

    Attached Files:

  13. Mar 24, 2016 #12

    haruspex

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    If that's the example to be followed then not mentioning the actual speeds is fine.
     
  14. Mar 24, 2016 #13
    ok thank you for your help.
     
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