# Review Conceptual Example 7 as background material for this problem. A jet transport has a weight of

## Question:

Review Conceptual Example 7 as background material for this problem. A jet transport has a weight of 1.00 × 106 N and is at rest on the runway. The two rear wheels are 15.0 m behind the front wheel, and the plane’s center of gravity is 12.6 m behind the front wheel. Determine the normal force exerted by the ground on

(a) The front wheel and on

(b) Each of the two rear wheels.

Conceptual Example 7

Figure 9.12a shows a stationary cargo plane with its front landing gear 9 meters off the ground. This accident occurred because the plane was overloaded toward the rear. How did a shift in the center of gravity of the loaded plane cause the accident?

Reasoning and Solution Figure 9.12b shows a drawing of a correctly loaded plane, with the center of gravity located between the front and the rear landing gears. The weight W(vector) of the plane and cargo acts downward at the center of gravity, and the normal forces FN1(vector) and FN2(vector) act upward at the front and at the rear landing gear, respectively. With respect to an axis at the rear landing gear, the counterclockwise torque due to FN1(vector) balances the clockwise torque due to W(vector), and the plane remains in equilibrium.

Figure 9.12c shows the plane with too much cargo loaded toward the rear, just after the plane has begun to rotate counterclockwise. Because of the overloading, the center of gravity has shifted behind the rear landing gear. The torque due to W(vector) is now counterclockwise and is not balanced by any clockwise torque. Due to the unbalanced counterclockwise torque, the plane rotates until its tail hits the ground, which applies an upward force to the tail. The clockwise torque due to this upward force balances the counterclockwise torque due to W(vector), and the plane comes again into an equilibrium state, this time with the front landing gear 9 meters off the ground.

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