$6\mathrm{.}11$ A wheel tractor$-$scraper is operating on a level grade. Assume no power derating is required for equipment condition,

altitude, and temperature. Use equipment data from Fig. $6\mathrm{.}7.$

a$.$ Disregarding traction limitations$,$ what is the maximum value of rolling resistance $($in $l\frac{b}{t}on)$ over which the fully loaded

unit can maintain a speed of $10$ mph $?$

b$.$ What minimum value of coefficient of traction between the tractor wheels and the traveling surface is needed to satisfy

the requirements of part a$?$ For the fully loaded condition, $50\%$ of the weight is distributed to the drive axle. Operating

weight of the empty scraper is $89,973\mathrm{.}0lb.$