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!

Question regarding motion of vehicles

  1. Sep 24, 2009 #1
    1. Question:

    You are driving your car (take the direction to be positive) at 20m/s. A van is following you, also at 20m/s. When you see a fog bank ahead of you, you hit the brakes (take this to be the time t=0). The driver of the van sees your brake lights and applies her brakes 1 second later. Both you and the van, when braking, have a constant acceleration of 5m/s^2 magnitude until coming to a stop.

    After the van and the car have both stopped, are they further apart, closer together, or the same distance apart than at t=0? How much, in meters, has the distance between them changed?

    How far behind the car should the van be at t=0 to avoid a collision?

    2. Relevant equations:

    Area under the graph of velocity versus time = distance travelled
    s=s(initial)+v(initial)*t+(0.5)(a)(t^2)

    3. The attempt at a solution

    The van and the car are further apart after stopping.
    Distance travelled by car after t=0:
    (0.5)(4^2)(-5)=40m
    Distance travelled by van after t=0:
    (4)(20)+(0.5)(-5)(4^2)+20=60m
    Change in distance=60m-40m=20m

    The car and the van have to be at least 20m apart to avoid collision.

    p/s: Is this correct? Thank you very much! =)
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Can you offer guidance or do you also need help?
Draft saved Draft deleted



Similar Discussions: Question regarding motion of vehicles
Loading...