- #1

clope023

- 992

- 132

**[SOLVED] Automobile Power**

## Homework Statement

A truck engine transmits 28.0kW(37.5hp ) to the driving wheels when the truck is traveling at a constant velocity of magnitude 60.0km/h ( 37.3mi/h) on a level road.

a) resistance force? P = Fv, P/v = F = 1680N

this is where I have trouble

b) Assume that 65% of the resisting force is due to rolling friction and the remainder is due to air resistance. If the force of rolling friction is independent of speed, and the force of air resistance is proportional to the square of the speed, what power will drive the truck at 30.0 ? Give your answer in kilowatts .

## Homework Equations

P = Fv

## The Attempt at a Solution

so it says the forces acting are 65% of the resisting force (.65*1680 = 1092) and the air resistance is the square of the speed, so I used (with speed in 8.3m/s):

P = Fv = 1092(8.3^3) = 624,391 W = 624kw wrong

also tried:

P = Fv = (1092+8.2^2)8.3 = 9,621 W = 9kW wrong

I think I'm using the wrong force, any help is appreciated.