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!

Car Coming to a Stop w/ Kinetic Energy and Friction

  1. Nov 14, 2014 #1
    1. The problem statement, all variables and given/known data
    An 1100-kg car traveling at 24 m/s coasts through some wet mud in which the net horizontal resistive force exerted on the car from all causes (mostly the force exerted by the mud) is 1.7 x 10^4 N. Determine the car’s speed as it leaves the 18-m-long patch of mud.

    [itex]m = 1,100 kg[/itex]
    [itex]v_i = 24 m/s[/itex]
    [itex]\vec F = -1.7x10^4 N[/itex]
    [itex]\vec s = 18 m[/itex]

    2. Relevant equations
    [itex]KE_i = \frac {1}{2} mv_i^2[/itex]
    [itex]\Delta KE = \vec F \vec s[/itex]
    [itex]\Delta KE = KE_f - KE_i \Rightarrow KE_f = \Delta KE + KE_i \Rightarrow \frac {1}{2} mv_f^2 = \Delta KE + KE_i[/itex]
    [itex]\Rightarrow v_f = \sqrt {\frac {2(\Delta KE + KE_i)}{m}}[/itex]

    3. The attempt at a solution
    [itex]KE_i = \frac {1}{2} (1,100 kg)(24 m/s)^2 = 316,800 J[/itex]
    [itex]\Delta KE = (-1.7x10^4 N)(18 m) = -306,000 J[/itex]
    [itex]\Rightarrow v_f = \sqrt {\frac {2((-306,000 J) + (316,800))}{(1,100 kg)}} = 4.4312 m/s \sim 4.4 m/s[/itex]

    Thank-you
     
  2. jcsd
  3. Nov 14, 2014 #2

    NascentOxygen

    User Avatar

    Staff: Mentor

    That looks right.

    And it means the title of this thread is a bit misleading.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted