In a lab, a student drags a shoe across the floor at constant speed. If the coefficient of static friction between the floor and
the shoe is 0.30N and the coefficient of kinetic friction is 0.25, what is the maximum friction force on a 2N shoe before it begins to move? A) 0.5 N
B) 0.6 N
C) 6.67 N
D) 8 N
<span>B) 0.6 N
I suspect you have a minor error in your question. Claiming a coefficient of static friction of 0.30N is nonsensical. Putting the Newton there is incorrect. The figure of 0.25 for the coefficient of kinetic friction looks OK. So with that correction in mind, let's solve the problem.
The coefficient of static friction is the multiplier to apply to the normal force in order to start the object moving. And the coefficient of kinetic friction (which is usually smaller than the coefficient of static friction) is the multiplied to the normal force in order to keep the object moving. You've been given a normal force of 2N, so you need to multiply the coefficient of static friction by that in order to get the amount of force it takes to start the shoe moving. So:
0.30 * 2N = 0.6N
And if you look at your options, you'll see that option "B" matches exactly.</span>
