How Does Friction Affect the Acceleration of a Moving Bureau?

[MathewsMD]

A bureau rests on a rough horizontal surface (μ_s=0.50, μ_k=0.40). A constant horizontal force, just sufficient to start the the bureau in motion, is then applied. The acceleration of the bureau is _____?

Attempt:

Fapp = ma = mgμ_s if there is no acceleration. But since there is movement, it must be the smallest value of a possible. We also know Fapp is just slightly greater than f_s, right?

F_NET = ma = Fapp - f_s
ma = Fapp - mgμ_s

Well, I'm stuck here. I don't know what the value of a would be, I would just guess it's the smallest possible value. But how would that be figured out from what is give? Any help would be amazing! :)

 

[CWatters]

The coefficient of static friction is higher then the coefficient of dynamic friction.

The force required to start it moving is that required to overcome static friction = mgμ_s and that's the constant horizontal force that continues to be applied for the rest of the problem.

Once moving the net forces acting on the bureau is therefore the applied force mgμ_s minus the force due to kenetic friction mgμ_k

Then apply Newton.

 

[tiny-tim]

Hi MathewsMD!

You find F_app as the minimum F that gives you movement, using µ_s.

Then you use that same F_app and µ_k to find the acceleration.