To measure the static friction coefficient between a 1.9 kg block and a vertical wall, the setup shown in the?

Question

To measure the static friction coefficient between a 1.9 kg block and a vertical wall, the setup shown in the drawing is used. A spring (spring constant = 470 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. If the spring in such a setup is compressed by 0.053 m, what is the coefficient of static friction?

Answer 1

It's a bit hard to tell without the drawing, but I think I can see how this is set up. Start by calculating the applied force, based on what you know about the spring. F = -kx, so the applied force is 0.053 m, the compression of the spring, multiplied by 470 N/m, the spring constant; the negative sign can be ignored in this case, because we're dealing with magnitudes, not vectors. Now, if the block doesn't slip, the upwards friction force must equal the downwards gravitational force. Call the spring force F_spring. The friction force, then, would be F_friction = u*F_spring, where u is the unknown coefficient of static friction. The force of gravity, the weight, would be W = mg, where m is the 1.9 kg mass of the block and g is gravity, 9.8 m/s^2. So F_friction = W ==> u*F_spring = mg ==> ukx = mg, and u is your only unknown.

Answer 2

Is the direction of the applied force above or below the horizontal .. or maybe, to the vertical ?