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Homework Help: What is the deceleration of the vehicle?

  1. Oct 18, 2009 #1
    1. I am looking to verify my calculation. Question A vehicle of mass 5Tonnes is travelling with a velocity of 80kmh-1 if it needs to stop within a dstnace of 0.5 km using a constant braking force what is the deceleration of the vehicle

    2. V^2 = 2xSxA, A=V^2 / 2S

    3. A=V^2/2s
    80kmn = 22.222ms
    Deceleration = - 0.494
  2. jcsd
  3. Oct 18, 2009 #2


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    Re: Deceleration

    Looks good :smile:

    Welcome to PF.
  4. Oct 19, 2009 #3
    Re: Deceleration

    appreciated thanks
  5. Oct 19, 2009 #4
    Re: Deceleration

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    IET » Student and apprentice discussion forum » Calculation check Topic Title: Calculation check
    Topic Summary: Deceleration
    Created On: 18 October 2009 06:11 PM
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    18 October 2009 06:11 PM


    Posts: 11
    Joined: 28 September 2009

    Can anyone give this the once over make sure I have the formula calcs etc right

    Vehicle mass 5 Tonnes travelling with a velocity 80kmh. It needs to stop with in 0.5km using constant braking force

    (80kmh = 80x1000/3600 = 22.2m/s)

    a=(v^2-u^2) / 2s
    a= 0.494ms
    as Deceleration = -0.49

    Just want to check I am on the right line
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    19 October 2009 01:45 PM


    Posts: 579
    Joined: 14 September 2001

    It's a very good start. Perhaps you could add a few explanatory notes to your working so it can be checked properly.

    E.g., "Deceleration80kmh = 80x1000/3600 = 22.2m/s)" should be 'velocity' or 'speed' in m/s.

    Please have another go.

    Kind regards

    tony sung
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    19 October 2009 07:11 PM


    Posts: 11
    Joined: 28 September 2009

    Apologies that should have been Velocity 22.2ms

    My concern is whilst working out time taken

    V/A=T, 22.2/0.4938 = 45s

    I checked using a Velocity, Time distance calculator on the net and it calculates 22.5s

    Therefore was I correct in using 2s in my initial calculation, it appears to be correct when I transformed the formula
  6. Oct 19, 2009 #5


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    Re: Deceleration

    Yes, 2s was correct since the equation is

    v2 = 2 s a​

    22.5 sec would be the time to go 500 m at a constant velocity (no deceleration) of 22.2 m/s. But in that case the vehicle would not come to a stop, as stated in the problem.
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