I am wondering if someone could guide me on this. I am getting a vf of 4.6m/s, which can't be right, considering vi is only 3.8m/s.(adsbygoogle = window.adsbygoogle || []).push({});

A box slides across a frictionless floor with an initial speed v = 3.8

m/s. It encounters a rough region where the coefficient of friction is

µk = 0.7. If the strip is 0.52 m long, with what speed does the box

leave the strip?

My thoughts:

F=µk*N=µk*g*m=6.867*m

vi=3.8 m/s

Using work-energy theorem:

F*d = .5*m*vf^2 - .5*m*vi^2

6.867*d*m = m*(.5*vf^2 - .5*vi^2)

m's cancel

6.867*.52 + .5*vi^2 =.5*vf^2

3.4335 + .5*(3.8)^2 =.5*vf^2

(3.4335 + 7.22)*2=vf^2

sqrt (21.307) = vf

4.62 = vf

Ridiculous. What am I doing wrong?

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# Homework Help: Going through a rough spot

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