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Finding Thrust from aircraft, need rolling friction

  1. Sep 26, 2008 #1
    1. The problem statement, all variables and given/known data
    An Airbus A320 jetliner has a takeoff mass of 75,000 kg. It reaches its takeoff speed of 82 m/s in 35s.
    Find the Thrust of the engines, don't worry about air resistance, but rolling friction is substantial.

    2. Relevant equations
    Fnet=mass*acceleration
    a=(82/35)
    mass=75000
    rolling_friction=mu*n (n=normal force) (mu=friction coefficient)
    Fnetx=rolling_friction-thrust
    Fnety=n-weight(m*g (gravity))
    n=mg
    3. The attempt at a solution

    I got as far as:
    Thrust=mu(m*g)-m*a

    I know that I need to solve for mu, but I can't seem to find a good way to further relate the equations.
     
  2. jcsd
  3. Sep 26, 2008 #2

    mgb_phys

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    Remember forces add. so
    Force (thrust) = m * a + friction
    You know m * a so you can separate out the friction force.
    And since you know the mass you can get the co-efficeint.

    I think this is a case where you are better putting in the numbers you know before re-arranging the equations, it should be obvious.
     
  4. Sep 26, 2008 #3
    thanks for the help. though, i'm having trouble getting the friction coefficient by itself. i thought it was mu= F/mg, though i'm not sure if that's right.
     
  5. Sep 26, 2008 #4

    mgb_phys

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    Friction = u * normal force = u * weight = u * mg
     
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