Force of a spring and static friction

AI Thread Summary
The discussion focuses on calculating the force of static friction acting on a backpack resting on a table, which is attached to a spring. The backpack weighs 54.3N, and the spring has a force constant of 200N/m, stretched by 1.50cm. The participant initially attempted to find the coefficient of static friction using the equation mus=kx/N but encountered confusion. They later realized the correct approach was to equate the force of static friction directly to the spring force, leading to the conclusion that fs=kx. The resolution highlights the importance of correctly applying physics equations in static scenarios.
matt@USA
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Homework Statement


A backpack full of books weighing 54.3N rests on a table in a physics laboratory classroom. A spring with a force constant of 200N/m is attached to the backpack and pulled horizontally, as indicated in the figure. If the spring is pulled until it stretches 1.50cm and the pack remains at rest, what is the force of friction exerted on the backpack by the table? Imagine the spring being pulled with a force to the -x, and the force of static friction going in the +x direction.

Homework Equations


I know that the force of the spring is equal to F=kx, the force of static friction is mus*Normal force. I tried to find the mus to solve the equation but I was wrong. I got the sum of the net force in the x direction as fs-F=0, and the sum of the net force in the y direction as N-mg=0.


The Attempt at a Solution


The final equation I used to try to solve for mus was mus=kx/N, with 200N/m being my k, .015m being my x, and 54.3N being my N. Can someone please tell me where, or how I messed up?
 
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matt@USA said:

Homework Statement


A backpack full of books weighing 54.3N rests on a table in a physics laboratory classroom. A spring with a force constant of 200N/m is attached to the backpack and pulled horizontally, as indicated in the figure. If the spring is pulled until it stretches 1.50cm and the pack remains at rest, what is the force of friction exerted on the backpack by the table? Imagine the spring being pulled with a force to the -x, and the force of static friction going in the +x direction.

Homework Equations


I know that the force of the spring is equal to F=kx, the force of static friction is mus*Normal force. I tried to find the mus to solve the equation but I was wrong. I got the sum of the net force in the x direction as fs-F=0, and the sum of the net force in the y direction as N-mg=0.


The Attempt at a Solution


The final equation I used to try to solve for mus was mus=kx/N, with 200N/m being my k, .015m being my x, and 54.3N being my N. Can someone please tell me where, or how I messed up?

How far off was your answer? 200 N/m is a pretty weak spring. 200 kN/m would be a good solid spring.
 
NM, I figured it out. The correct equation was fs=F, and F=kx, so fs=kx!
 

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