Class I Help HW3 Begin Date:9/20/2018 12:00:00 AM -- Due Date: 10/2/2018 11:59:0

Question

Class I Help HW3 Begin Date:9/20/2018 12:00:00 AM -- Due Date: 10/2/2018 11:59:00 PM End Date: 12/11/2018 11:59:00 PM (890) Problem 10: Helicopter blades withstand tremendous stresses. In addition to supporting the weight of a helicopter, they are spun at rapid rates and experience large centripetal accelerations, especially at the tip Randomized Variables r=4.2 m pm 270 rpm , 50% Part (a) Calculate the centripetal acceleration at the tip of a 4.2 m long helicopter blade that rotates at 270 rev min in m/s ac 3.37 103 ac-3370 Correct! e 50% Part (b) Compare the linear speed of the tip with the speed of sound (taken to be 340 ms sound. Give your answer in percent of the speed of Grade Summary Potential Submissions Vrhip Vsound (%)- 6% 94% sin() | cos() | tan() | (1)17 8 cotan asinacos0 atan acotan0 si cosh0 tanhcotanh0 Attempts remaining: 9 1% per attempt) detailed view 196 1% 1% 1% 0 END Degrees Radians DELI CLEAR Submit Hint Feedback Hints: 0% deduction per hint. Hints remainng: Feedback: 0% deduction per feedback.

Explanation / Answer

part A

centripetal accleration (ac) = 3370m/s^2

part B

use v = rW

from linear accleration a = r W^2

here angular velocity W = 270 *2pi/60

W = 28.26 rad/s

Vtip = RW

Vtip = 4.2 * 28.26

Vtip/Vsound = (4.2*28.26)/(340)

Vtip/Vsound = 0.35

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