A computer scientist has dropped a tiny pizza crumb onto a magnetic disk. (A mag

Question

A computer scientist has dropped a tiny pizza crumb onto a magnetic disk. (A magnetic disk is a rotating disk used to record data.) Later, when it's turned on, the disk is rotating at 88 revolutions per second (to 2 significant figures) about its axis, which is vertical. The coefficients of kinetic and static friction between pizza crumbs and the disk are 1.3 and 1.6 respectively. (No, we don't know how or why they were measured: geeks are geeks!) What is the maximum radius from the axis at which a pizza crumb will stay on the disk?

Explanation / Answer

w = 88 rev/min

= 88*2*pi/60

= 9.21 rad/s

Force required = m*r*w^2

mue_s*m*g = m*r*w^2

r = mue_s*g/w^2

= 1.6*9.8/9.21^2

= 0.185 m or 18.5 cm

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