514_Physics ProblemsTechnical Physics

514_Physics ProblemsTechnical Physics - 516 Sound Waves ja...

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516 Sound Waves P17.55 v d t = 2 : d vt == × = 2 1 2 650 10 185 601 3 .. . ms s km ej af P17.56 (a) The speed of a compression wave in a bar is v Y × ρ 20 0 10 7860 504 10 10 3 . . Nm kg m 2 3 . (b) The signal to stop passes between layers of atoms as a sound wave, reaching the back end of the bar in time t L v × 0800 159 10 4 . . m 5.04 10 m s s 3 . (c) As described by Newton’s first law, the rearmost layer of steel has continued to move forward with its original speed v i for this time, compressing the bar by Lv t i × = × = −− 12 0 1 59 10 1 90 10 1 90 43 . . s m mm bg . (d) The strain in the rod is: L L = × 190 10 238 10 3 3 . . m 0.800 m . (e) The stress in the rod is: σ = F H G I K J × = Y L L 20 0 10 2 38 10 476 10 3 MPa 2 e j . Since > 400 MPa , the rod will be permanently distorted. (f) We go through the same steps as in parts (a) through (e), but use algebraic expressions rather than numbers: The speed of sound in the rod is v Y = . The back end of the rod continues to move forward at speed v i
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