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Distance and acceleration problem

  1. May 15, 2016 #1
    1. The problem statement, all variables and given/known data
    A police radar has an effective range of 1.0 km, and a motorist's radar detector has a range of 1.9 km. The motorist is going 120 km/h in a 80 km/h zone when the radar detector beeps. At what rate must the motorist decelerate to avoid a speeding ticket?

    2. Relevant equations
    v^2=u^2+2as
    v=288m/s
    u=432m/s
    a=
    t=
    s=900m

    3. The attempt at a solution
    82944=186624+(2*a*900)

    (82944-186624)/900/2

    =57.6m/s^2
     
  2. jcsd
  3. May 15, 2016 #2

    Charles Link

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    Homework Helper

    60 m.p.h.=88 ft/sec. Your velocities of 288 m/sec and 432 m/sec are much too high. 1 meter is slightly greater than 3 ft.
     
  4. May 15, 2016 #3
    Ahh of course, thank you for your help.
     
  5. May 15, 2016 #4
    check the calculation;
    for example 80 km/h = 80 x 10^3 m/ (60x60) sec.= 800/36 m/s=200/9 m/s and you are writing v=288m/s so correct it and other velocity also.
     
  6. May 15, 2016 #5

    SteamKing

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    Staff Emeritus
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    Interesting fact: the speed of sound at sea level is about 340 m/s, also known as Mach 1.

    If you're going Mach 1 in an 80 kph zone, no crummy Fuzz is going to catch you. o_O
     
  7. May 15, 2016 #6
    Thank you.
     
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