problem02_77 solution

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

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2.77: Let t 1 be the fall for the watermelon, and t 2 be the travel time for the sound to return. The total time is s 5 . 2 2 1 = + = t t T . Let y be the height of the building, then, . 2 s 2 1 2 1 and t v y gt y = = There are three equations and three unknowns. Eliminate t 2 , solve for t 1 , and use the result to find y . A quadratic results: . 0 s 1 s 2 1 2 1 = - + T v t v gt If . then , 0 2 4 2 2 a ac b b t c bt at - ± - = = + + m 850 s) 5 2 )( s m 340 ( and , s m 340 , s m 9 . 4 2 1 , Here, s s 2 1 - = - = - = = = = = = . T v c v b g a t t Then upon substituting these values into the quadratic formula,
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Unformatted text preview: ) s m 9 . 4 ( 2 m) 850 )( s m 9 . 4 ( 4 ) s m (340 ) s m 340 ( 2 2 2 1--±-= t ( 29 ( 29 ( 29 s 42 . 2 2 m/s 9 . 4 2 s m 7 . 363 s m 340 1 = = ±-t . The other solution, –71.8 s has no real physical meaning. Then, . m 6 . 28 ) s 42 . 2 )( s m 8 . 9 ( 2 2 2 1 2 1 2 1 = = = gt y Check: s, 08 . ) s m (340 m) 6 . 28 ( = the time for the sound to return....
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