39. A \( 1000-\mathrm{N} \) bobsled leaves a horizontal track with a speed of \( 30 \mathrm{~m} / \mathrm{s} \). It then moves onto a horizontal track lightly sprinkled with sawdust and comes to a stop in a distance of \( 150 \mathrm{~m} \). Find the coefficient of kinetic friction between the runners of the sled and the sawdustcovered surface.
