Block on Wall Static Friction (Springs)

  • #1

Homework Statement

To measure the static friction coefficient between a 1.64-kg block and a vertical wall, the setup shown in the drawing below is used. (The dots are only there because spaces didn't work)
A spring (spring constant = 500 N/m) is attached to the block. Someone pushes on the end of the spring in a direction perpendicular to the wall until the block does not slip downward. The spring is compressed by 0.0400 m. What is the coefficient of static friction?

K = 500n/m
m = 1.64kg
x = 0.0400m

Homework Equations

I know that the force by the spring pressing against the block is 20N since i used F =kx
I also know that the force of gravity is 16.1N

The Attempt at a Solution

I've attempted finding force by the spring on the block = 20N
Force of gravity = 16.1N
then subbing the two in.
Ff = µFn
20 = µ(16.1)
µ = 1.24

But that's not the right answer.
Doesn't it only matter with the forces in the direction of motion?
so since the block would be falling, how does the spring come into play?
I'm kind of confused
  • #2
Hi Hypnos_16! :smile:
Ff = µFn
20 = µ(16.1)

erm :redface: … your numbers don't fit your letters :wink:
  • #3
How do you mean?
The force of gravity is the only thing working in the y direction so Fn = Mg
And i figured the force of friction would be the force required to keep it from moving.
  • #4
16.1 = µ(20) :wink:
  • #5
You're joking me! wow. I feel like an idiot now...and yep, that's the right answer. Thanks man!