Boat mass 460kg,constant speed 8.9m/s,propeller force 745N,engine shuts off,resistiveforce constant whats d&s?

Question

Boat coasts to a halt. Assume-contrary to fact-that the resistive force due to the water is constant, inderpendent of the boats 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?

Answer 1

Constant speed mean force is balanced, i.e., propulsion equals drag. You have the kinetic energy, which is work, which is force * distance

Answer 2

♠ since she is moving with constant speed friction force also f=745N;
♣ now off! her speed will slow down and look like:
v=v0-at, here v0=8.9m/s, a=f/m=1.62m/s^2 is deceleration,
m=460kg, t is time; hence t=(v0-v)/a;
if final v=0 then t=v0/a =5.4953 s;
♦ while slowing down to stop she’ll pass d=v0*t –0.5a*t^2;
borrow t and a from ♣ then
d=(v0^2-0.5*v0^2)/a =0.5v0^2/a =24.454 m;