Total power developed and kinetic energy

[thoradicus]

Homework Statement

A horizontal force of 2000N is applied to a vehicle of mass 400kg which is initially at rest on a horizontal surface. If the total force opposing motion is constant at 800N, calculate
(i)the acceleration of vehicle
(ii)the kinetic energy 5s after force is applied
(iii)the total power developed after 5s the force is applied

Homework Equations

F=ma
P=W/t
1/2(m)(v)^2
P=Fv
v=u+at

The Attempt at a Solution

(i)2000-800=400a
a=3ms^-2
(ii)v=(3)(5)
=15m/s
K.E=0.5(400)(15)^2
=45000W
(iii) This part I am not sure of...i tried adding 2 powers together:
P=Fv
=(1200)(15)=18000
18000+(45000/5)=27000 but its not the right awnser

 

[LawrenceC]

Power is force times velocity.

 

[Serac]

You have the acceleration, and you have a time. The object is initially at rest, so it's velocity is: 5a.

From this velocity, you must multiply it by the net force on the object.