Question 536797
If the horsepower p required to drive a speedboat through water is directly proportional to the cube of the speed v of the boat,
 what change is horsepower would be required to double the speed of the boat?
:
P = v^3
"what change is horsepower would be required to double the speed of the boat?"
P = (2v)^3
P = 8v^3
: 
Power has to be increased by a factor of 8