# Springs and static friction

1. Oct 7, 2007

### bc64846

a 52 N backpack is laying on a table with a spring attached to one side of it where force is applied and the spring stretches. The backpack begins to slide when the spring (k= 150 N/m) stretches by 2.50 cm. What is the coefficient of static friction between the backpack and the table?

i set up a freebody diagram, but i guess i'm just confused about the weight given in N. I have only had problems dealing with kg. I set up adding all forces in the x and y direction and got:

-F + fs = ma(x direct)
-Fg + FN = ma(y direct)

FN is normal force, fs is static force

I got the F by using F= -kx and got 3.75N

2. Oct 11, 2007

### phlegmy

if the spring stretches 2.5cm =.025m so the force is
150N/m * .025 = 3.75n

now this is the force reqired to just overcome the static friction

so assuming the table is horizontal the reaction force is 52N

now 3.75N= cof of frict * 52N

soooooooooooooooo..........................

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