Conservation of Energy, Car Driving with Drag Force

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Homework Help Overview

The problem involves a 710kg car driving at a constant speed of 23m/s while experiencing a drag force of 500 N. The discussion focuses on determining the power required from the car's engine to maintain this speed on level ground and while driving up a hill with a slope of 2.0 degrees.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the relationship between power, force, and speed, questioning how to approach the problem without time information. Some suggest using the constant speed condition to relate forces and power. Others propose calculating additional forces acting on the car when driving uphill.

Discussion Status

The discussion includes various interpretations of how to calculate power under the given conditions. Some participants have provided insights into the relationship between forces and power consumption, while others express uncertainty about the problem's requirements. There is no explicit consensus, but several productive lines of reasoning have been explored.

Contextual Notes

Participants note the lack of time information in the problem, which complicates the calculation of power. Additionally, the original poster has not engaged further in the discussion since the initial post.

David Mordigal
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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 2.0o? 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.
 
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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?
 
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.
 
This question is probably moot by now, given that it was first posted in Nov. 2014 and the OP never replied.
 
OK, thanks
 

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