Problem 877 Part A The squarethreaded screw has a mean diame

Problem 8.77 Part A The square-threaded screw has a mean diameter of 19 mm and a lead of 5 mn. The weight of the plate A is 5 lb. (Figure 1) Determine the smallest coefficient of static friction between the screw and the plate so that the plate does not travel down the screw when the plate is suspended as shown. Express your answer using three significant figures. vec . : 1.838 | Submit My Answers Give Up Figure * Incorrect; Try Again; 5 attempts remaining Continue

Solution

mean diametre = 19 mm, => radius r = 9.5mm

lead l = 5 mm

screw is self locking when friction angle( a) is greater than helix angle (b) => a>b   

Tan b = ( L / 2 * pi * r ) = 5 / (2 * 3.17 * 9.5)

=> b = 4.788 degrees

bt friction angle is tan inverse of friction coefficient

mu = tan (friction angle) = tan 4.788 = 0.0837

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