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!

Homework Help: Circular motion of a subway train

  1. May 22, 2008 #1
    1. The problem statement, all variables and given/known data
    A subway train rounds an unbanked curve at 67 km/h. An unused strap makes an angle of 15 degrees to the vertical. What is the radius of the turn. The book answer is 132 m.

    2. Relevant equations
    F = ma = mv^2/r

    3. The attempt at a solution
    A free-body diagram shows a normal force pointing up 75 degrees from the horizontal axis. An mg force points down along the y axis.

    Along the x axis N sin 15 degrees = mv^2/r.

    r = mv^2/N sin 15 degrees.

    Along the y axis N = mg cos 15 degrees.

    Substituting, r = mv^2/mg sin 15 degrees/cos 15 degrees = v^2 / g tan 15 degrees

    r = (67)^2 km^2/ H^2 / 9.8 m/s^2 / 3600 s^2/ h^2 * 1000 m/km / .268 = 475 m
  2. jcsd
  3. May 22, 2008 #2

    Doc Al

    User Avatar

    Staff: Mentor


    You mean: N cos 15 degrees = mg


    First convert 67 km/h to m/s.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook