InterviewSolution
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InterviewSolution
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A block is mass `m` is dropped from the fourth of an office building and hits the sidewalk below at speed `v` . From what floor should the block the dropped to double that impact speed?A. the either floorB. the thenth floorC. the twelfth floorD. the sixteenth floor |
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Answer» Correct Answer - D As the back falls freely, only the conservative gravitation force acts on it. Therefore, mechainical energy is conservate, or `KE_(f) = KE_(f) + PE_( C)` Assuming that the block is releasedfrom rest `(KE_(i) = 0)` and taking `y = 0` at ground level `(PE_(f) = 0)` we have that `KE_(f) = PE_(i)` or `(1)/(2) mv_(1)^(2)` = mgy and `y_(i) = (v_(f)^(2))/(2g)` Thus, to double the final speed, it is necessary to increase the initial height by a factor of four. |
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