A power boat of mass 495 kg is cruising at a constant speed of 8.9 m/s. The propeller provides a drive force of 780 N. The driver of the boat shuts off the engine, and the boat coasts to a halt. Assume-contrary to fact-that the resistive force due to the water is constant, independent of the boat's speed.

Question

A power boat of mass 495 kg is cruising at a constant speed of 8.9 m/s. The propeller provides a drive force of 780 N. The driver of the boat shuts off the engine, and the boat coasts to a halt. Assume-contrary to fact-that the resistive force due to the water is constant, independent of the boat's speed.
(a) How far does the boat coast?
 m
(b) How much time does it take for the boat to come to rest after the engine is turned off?

drwls · Answer

a) Set F*X equal to the initial kinetic energy and solve for X. X is the distance and f is the friction force, which is here assumed to equal the propeller force while running at full speed, 780 N

b) Divide X by the average speed, V/2.