# Homework Help: Finding Thrust from aircraft, need rolling friction

1. Sep 26, 2008

### jheld

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. Sep 26, 2008

### mgb_phys

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.

3. Sep 26, 2008

### jheld

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.

4. Sep 26, 2008

### mgb_phys

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