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!

Kinematics Acceleration (27)

  1. Jul 27, 2016 #1
    1. The problem statement, all variables and given/known data
    A train that runs 140 km / h requires about 700m to stop. Calculate the average acceleration of the train while braking.


    2. Relevant equations
    v: x/t



    3. The attempt at a solution
    v= x/t
    so t= x/v= 700m/ (38.89m/s)=18 s
    Now to find acceleration a= v/t
    a= 38,89m/s / 18s =2,160 m/s^2
    They're asking the average so 2,160 m/s2 is our initial acceleration
    therefore
    0-2,160 m/s^2 / (2) = -1,08024
    Is it the correct formula to use ? or is it wrong ???
     
  2. jcsd
  3. Jul 27, 2016 #2
    The equation you used for the velocity is correct only if the acceleration is zero (i.e., only if the velocity is constant).
     
  4. Jul 27, 2016 #3
    Oh I see. I think i've found out which kinematic equation to use .

    I tried this one
    initial velocity = 140 km/h (38,89 m/s)
    Final velocity = 0 m/s because its going to stop
    (vx)^2=(u)^2 + 2x a x700 m
    (38,89)^2=1400 x a
    a= -1512,34/ 1400
    a= -1,0802
     
  5. Jul 27, 2016 #4

    PeroK

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    That's correct. Can you think of a way to confirm that answer is right?
     
  6. Aug 3, 2016 #5
    My workbook says so
     
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: Kinematics Acceleration (27)
Loading...