problem04_42

University Physics with Modern Physics with Mastering Physics (11th Edition)

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4.42: a) The velocity of the spacecraft is downward. When it is slowing down, the acceleration is upward. When it is speeding up, the acceleration is downward. b) speeding up: F w and the net force is downward slowing down: F w < and the net force is upward c) Denote the y -component of the acceleration when the thrust is 1 F by 1 a and the y - component of the acceleration when the thrust is 2 F by 2 a . The forces and accelerations are then related by . , 2 2 1 1 ma w F ma w F = - = - Dividing the first of these by the second to eliminate the mass gives , 2 1 2 1 a a w F w F = - - and solving for the weight w gives . 2 1 1 2 2 1 a a F a F a w - - = In this form, it does not matter which thrust and acceleration are denoted by 1 and which
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Unformatted text preview: by 2, and the acceleration due to gravity at the surface of Mercury need not be found. Substituting the given numbers, with y + upward, gives N. 10 . 16 ) s / m 80 . ( s / m 20 . 1 ) N 10 . 25 )( s / m 80 . ( ) N 10 . 10 )( s / m 20 . 1 ( 3 2 2 3 2 3 2 × =--×--× = w In the above, note that the upward direction is taken to be positive, so that 2 a is negative. Also note that although 2 a is known to two places, the sums in both numerator and denominator are known to three places....
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This document was uploaded on 02/04/2008.

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