Conservation of Energy, Car Driving with Drag Force

[David Mordigal]

Homework Statement

A 710kg car drives at a constant speed of 23m/s . It is subject to a drag force of 500 N. What power is required from the car's engine to drive the car (a) on level ground? (b) up a hill with a slope of 2.0^o? Express your answer to two significant figures.

Homework Equations

p = mv
P = ΔW/Δt (but no time information given)

The Attempt at a Solution

I am not sure where to begin. I understand that power is the change in work with respect to time, but there is no time information given in the problem, so I am a little lost.

 

[SteamKing]

The car is moving on level ground and up the hill at constant speed. Speed has got time in it. Why can't you use that?

 

[dean barry]

Since constant speed is the situation, the for and against forces are equal.
On level ground the mass of the car doesn't come into it.
Then :
Power consumption ( Watts ) = force overcome (N) * speed (m/s)
(applies to constant or instantaneous speed only)
In the uphill problem, calculate the additional force acting against the car and down the slope due to gravity ( m * g * sine (2 ° ) ) and add to the 500 Newtons of drag, then calculate the power consumption.

 

[SteamKing]

This question is probably moot by now, given that it was first posted in Nov. 2014 and the OP never replied.

 

[dean barry]

OK, thanks