1. Limited time only! Sign up for a free 30min personal 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!

Physic Acceleration

  1. Aug 28, 2013 #1
    1. The problem statement, all variables and given/known data
    A car traveling 100 km/h is 200m away from a truck traveling 50 km/h (in the same direction)
    . Assuming constant braking acceleration, what is the minimum deceleration the car must have if it is not to hit the truck?

    2. Relevant equations
    I know acceleration is a = (Vf - vi)/t but I do not know how to get the acceleration/deceleration when there two object instead of just let a car moving.


    3. The attempt at a solution
    I know the Vi of the Car is = 27.8 m/s
    The Vf of the Car is 13.9 m/s (The acceleration of the truck is this so won't it be the final velocity of the car when it crash?)
    Distance of car travel = 200+x
    Distance of truck travel = x;

    Can someone guide me in the right direction? Thanks
     
  2. jcsd
  3. Aug 28, 2013 #2

    Zondrina

    User Avatar
    Homework Helper

    Notice that the distance between the car and truck is decreasing at a rate of 100km/h - 50km/h = 50km/h.

    Also note that 200m = 0.2km. These will help you find time.

    Using this you can determine the proper acceleration.
     
  4. Aug 28, 2013 #3
    I understand when you say the decrease in the distance due to the different in the vehicle speed but I can't think of how to find the time when the truck and car is constantly moving. Thank you
     
  5. Aug 28, 2013 #4

    Zondrina

    User Avatar
    Homework Helper

    Remember that when you're dealing with speed :

    $$v = \frac{Δd}{Δt}$$

    So that :

    $$Δt = \frac{Δd}{v}$$
     
  6. Aug 28, 2013 #5

    CAF123

    User Avatar
    Gold Member

    Put one car at an origin. Write its displacement as a function of time. Put the truck 200m along the x axis and then write its displacement as a function of time. Equate these to find the time to collision as a function of acceleration.
     
  7. Aug 28, 2013 #6
    Thank you for the replies guy.
    I came up with that since the truck will travel a certain distance before the car hit, the distance for the can can be dCar = 200m + x . Since x is the distance the truck travel, it can be represented as x = ((Vf + Vi)/2) * t - 200.
    since x = distance, x can be x = vt (velocity * time). Is this how to approach this problem without using relative velocity? I'm stuck after this part.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Physic Acceleration
  1. Physics acceleration (Replies: 6)

Loading...