Review Conceptual Example 7 in preparation for this problem. In tests on earth a lunar surface exploration vehicle (mass = 5.90 × 10³ kg) achieves a forward acceleration of 0.220 m/s². To achieve this same acceleration on the moon, the vehicle’s engines must produce a drive force of 1.43 × 10³ N. What is the magnitude of the frictional force that acts on the vehicle on the moon?

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 F_N1(vector) and F_N2(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 F_N1(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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EEDERAL PRESS (a) FN2 FN2 cg cg Axis Axis (b) (c) @AP/Wide World Photos