A power boat of mass 450 kg is cruising at a constant speed of 8.9 m/s. The propeller provides a drive force of 745 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.
How far does the boat coast??
How much time does it take for the boat to come to rest after the engine is turned off??
2007-09-30 16:40:40 · 2 answers · asked by Anonymous in Science & Mathematics ➔ Physics
because the speed is constant the drive force = water resistive force,
when the engine stops we 'll have a boat with initial speed equal to 8.9 m/s has a mass of 450 Kg and applied on it a reverse force equal to 745 N.
the acceleration will be =745/450 = -1.66 m/s^2
v2=v1+a*t
0=8.9-1.66*t
t=5.36 s.
to find the distance:
d=.5 a*t^2
2007-09-30 17:02:35 · answer #1 · answered by PowerX 2 · 0⤊ 0⤋
Since the boat is moving at a constant speed, you know that the water resistance is 745N. The easy way is to say that the boat has a kinetic energy of
Ke = (1/2)mv² = (1/2)450*8.9²=17,822.25 J
Since work = energy = F*d = 17,822.25 J and you know F=745, then
d = 17,822.25/745 = 29.92 meters.
Doug
2007-09-30 23:53:08 · answer #2 · answered by doug_donaghue 7 · 0⤊ 0⤋