Find the size of the force due to wind and rolling friction

[am08]

[SOLVED] Force Problem

The total mass is 2300kg (weight = 5072lbs). Find the size of the force due to wind and rolling friction when the van speed is 42.17mph (1mph= 0.447m/s).

This is the graph: http://capa-new.colorado.edu/msuphysicslib/Graphics/Gtype12/prob09a_1004minivan.gif"

F = ma

a = (speed 2 - speed 1)/(Time 2 - Time 1)

Converted mph to m/s: a = (26.82 - 18.85)/(23) = 0.3465 m/s^2

Now F = (2300*0.3465) = 797 N

What did I do wrong?

 

[Dick]

You didn't do much wrong. Your graph looks a bit nonlinear, but I don't see how they would expect you to read much more than a rough estimate off of it. Is that really the statement of the problem? 42.17mph!? Four decimal places?

 

[ohhi]

Take the slope over the entire range of the graph.

 

[am08]

That's what I'm assuming... they gave me the weight in lbs. do I need to incorporate that into my equations in any way or is that just unnecessary/useless info.

 

[am08]

ohhi thanks a lot !