The power P(measured in horse power, hp) needed to propel a boat is directly proportional to the cube of the speed s. An 80−hp engine is needed to propel a certain boat at 10 knots. Find the power needed to drive the boat at 15 knots.
P=ks3model80hp=k(10 knots)3Substitute the given, solve for kk=80hp(10 knots)3=80hp1000 knots3=225hp knots3
Then if s=15 knots,
P=ks3ModelP=225hpknots3(15 knots)3Solve for P, cancel out like termsP=270hp
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