Torque Question



A jet transport has a weight of 1.00x10^6 N and is at rest on the runway. The two rear wheels are 15m behind the front wheel, and the plane's center of gravity is 12.6m behind the front wheel. Determine the normal force exerted by the ground on the front whell and each of the two rear wheels.

Ok, so I drew a sketch. I've got front wheel, rear wheels, in between the two i have the center of gravity, pushing down with 1x10^6 N. Behind are the rear wheels pushing up with an FN and in front of it the front wheel is pushing up with an FN. There's 15 m of distance between them. The distance from the center of gravity to the front wheel is 12.6 m, to the back wheels it is 2.4 m. But now, I don't know what to do. I can't find Torque (r * F) because even though I have distances from the center of gravity (r) I don't know an F. That's what I'm trying to find...which I can't find without Torque. lol. Any help?


Science Advisor
Gold Member
First, let's call the normal force on the front wheel F_f and the normal force on one of the rear wheels F_r (assume each rear wheel has the same normal force exerted on it, but not equal to the normal force of the front wheel). All you have to do is sum the moments about the front wheel to find the force on each of the rear wheels.

0 = 12.6*W - 2*F_r*15

(where W is the weight of the transport)

If you need to find F_f, you could check the sum of the forces or do a moment balance about the rear wheel, e.g. 0 = F_f + 2*F_r - W

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