1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Car chase question

  1. Sep 23, 2007 #1
    1. The problem statement, all variables and given/known data
    A speeder traveling 110 km/h races past a cop car. The cop car is at rest and pursues at acceleration of 9km/h until it reaches its maximum speed of 170km/h until it catches up with the speeder. How long does it take the cop car to catch the speeder answer in units of seconds

    3. The attempt at a solution

    i know the distance the 2 travel is equal

    so for the speeder d = 110/t

    and for the cop car i should use what formula so that i can relate them to d=d

    so that 11/t = the distance formula for the cop car
     
  2. jcsd
  3. Sep 23, 2007 #2
    what should my next steps be?? please help me
     
  4. Sep 23, 2007 #3
    can someone point me in thee right direction so i can start tryin to solve this the correct way
     
  5. Sep 23, 2007 #4
    learningphysics can you help me
     
  6. Sep 23, 2007 #5

    learningphysics

    User Avatar
    Homework Helper

    I recommend first find out the distance between the two cars, when the cop car has reached 170km/hr...

    How long does it take the cop car to reach 170km/h? Over what distance does this happen?

    How long has the speeder travelled in this time?
     
  7. Sep 23, 2007 #6
    ok so the time for the cop car to get to 170 km/h is

    170/9 = 18.8888 is that in seconds then?

    so then in 18.88 seconds the otehr car would have gone .577133 km?
     
    Last edited: Sep 23, 2007
  8. Sep 23, 2007 #7

    learningphysics

    User Avatar
    Homework Helper

    What distance has the cop travelled in 18.888 seconds? What distance has the speeder driven in 18.888s?
     
  9. Sep 23, 2007 #8
    i am gettin screwed up becuz the speeds are in km/h and the time is in seconds GRRR i suck
     
  10. Sep 23, 2007 #9
    ok so am i right in my sayin it takes the cop 18.88 seconds to reach 170 km/h

    and then i converted 170 to km/s aand got .0472 km/s
    and i converted 110 km/h to km/s and got .03055 km/s

    then the distance the speeder went was .57713 km
    and the distance for the cop is what???
     
  11. Sep 23, 2007 #10

    learningphysics

    User Avatar
    Homework Helper

    Is the acceleration 9km/h per second? What exactly is the acceleration given?
     
  12. Sep 23, 2007 #11
    yes that is the acceleration
     
  13. Sep 23, 2007 #12

    learningphysics

    User Avatar
    Homework Helper

    For the cop, you'd use:

    d = v1*t + (1/2)at^2. here v1 = 0. convert 9km/hr per second into km/s^2...
     
  14. Sep 23, 2007 #13
    the distance the cop travels then is.445568 km after 18.88 seconds

    so now i knwo they are .131562 km apart at that time

    so now what do i do to solve for the time of the cop car to catch the speeder
     
  15. Sep 23, 2007 #14
    so i then get this

    cop ---- d+.131562 = .0472km/s (t)
    speeder ---- d = .03055km/s (t)

    so then i can say that .0472t - .131562 = .03055t ?????
     
  16. Sep 23, 2007 #15

    learningphysics

    User Avatar
    Homework Helper

    yes. that looks right... at the end remember to add 18.888s to whatever you get here to get total time.
     
  17. Sep 23, 2007 #16
    so the total time it takes to catch teh speeder is 26.7896 seconds

    now to find the total distance each car traveled i simply take

    d = .03055km/s (26.7896) or d +.131562 = .0472km/s (26.7896) ??????
     
  18. Sep 23, 2007 #17
    cuz if i do that the distances are different
     
  19. Sep 23, 2007 #18

    learningphysics

    User Avatar
    Homework Helper

    Take the speeder's velocity times the total time.
     
  20. Sep 23, 2007 #19
    one more question regarding car chases learning if u dont mind

    speeder goin 30.9 m/s

    cop accelerates at 2.49m/s squared

    how long until he catches speeder
     
  21. Sep 23, 2007 #20
    so again the distances and times are equal for the two cars correct?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Car chase question
  1. Car Chase Problem (Replies: 6)

  2. Chasing Car Problem (Replies: 7)

  3. A cop chasing a car (Replies: 2)

Loading...