How Is Static Friction Calculated on an Inclined Plane with a Spring?

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Homework Help Overview

The discussion revolves around calculating static friction on an inclined plane involving a spring. The problem involves a 2.0 kg box on a 65-degree incline, attached to a spring with a force constant of 360 N/m and a static friction coefficient of 0.22. Participants are attempting to determine the maximum stretch of the spring while keeping the box at rest.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants are discussing the forces acting on the box, including weight and friction, and how these relate to the spring's force. There are attempts to clarify how to calculate the force due to gravity on the incline and how to apply Hooke's Law. Some participants express confusion about the calculations and the correct approach to finding the necessary force.

Discussion Status

The discussion is ongoing, with participants exploring different interpretations of the forces involved. Some guidance has been offered regarding the need to consider the angle of the incline when calculating the component of weight acting down the slope. There is a lack of consensus on the correct method to find the force needed to stretch the spring.

Contextual Notes

Participants have noted discrepancies in the spring constant values mentioned and are questioning the assumptions made regarding the forces acting on the box. There is a focus on understanding the relationship between the weight of the box, the incline angle, and the static friction involved.

kiarrahannice
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A 2.0kg box rests on a plank that is inclined at a angle of 65 degrees above the horizontal. The upper end of the box is attached to a spring with a force constant of 360 N/m. If the coefficient of the static friction between the box and the plank is 0.22, what is the maximum amount the spring can be stretched and the box remain at rest?

Can someone show me how to complete this problem. The answer is 6.6cm however I don't know to get there. thanks
 
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kiarrahannice said:
A 2.0kg box rests on a plank that is inclined at a angle of 65 degrees above the horizontal. The upper end of the box is attached to a spring with a force constant of 360 N/m. If the coefficient of the static friction between the box and the plank is 0.22, what is the maximum amount the spring can be stretched and the box remain at rest?

Can someone show me how to complete this problem. The answer is 6.6cm however I don't know to get there. thanks

Welcome to PF.

How about you start the problem?

What forces will the spring need to balance?
 
I know that I have to find the required force and divide that by 295 N/m--I know I said 360 but it is 295 in order to find the maximum amount how would the 2.0kg box factor in.
 
kiarrahannice said:
I know that I have to find the required force and divide that by 295 N/m--I know I said 360 but it is 295 in order to find the maximum amount how would the 2.0kg box factor in.

The box has a weight.
The weight has friction.

At maximum distance you will rely on both to get the maximum elongation of the spring.

That of course will balance against the Hookes Law F = k*x for the spring.
 
still confused I'M thining I will get the answer if I do the following F/295

is that right and to find force would I do F=295/2.0?

Please fill in the blanks if you can
 
kiarrahannice said:
still confused I'M thining I will get the answer if I do the following F/295...

You will ultimately determine the distance that way, but you need to determine what F is.

So what is the weight of gravity down the incline?
And what is the additional force of friction that you will use to get it to stretch to max?
 
That is the problem I don't know how to find Force. I am assuming the additional force is .19 I put .22 in the problem. I was looking at something else. How do I find force so I can solve.
 
kiarrahannice said:
That is the problem I don't know how to find Force. I am assuming the additional force is .19 I put .22 in the problem. I was looking at something else. How do I find force so I can solve.

Before you go assuming forces and distances and guessing just work it out directly.

What is the weight of the box?

Weight is force.

How much of that weight is directed down the incline? You know the angle.
 
okay so the weight is 2.0kg so that's force right and the upper end is directed down the incline. and right the angle is 65 degrees still lost
 
  • #10
kiarrahannice said:
okay so the weight is 2.0kg so that's force right and the upper end is directed down the incline. and right the angle is 65 degrees still lost

2 kg is the mass

Weight is m*g.
 
  • #11
okay so force would be (9.81)(2.0)? Is that correct? and if it is if I divide that by 295 I do not get 6.6
 
  • #12
kiarrahannice said:
okay so force would be (9.81)(2.0)? Is that correct? and if it is if I divide that by 295 I do not get 6.6

That's the weight all right.

But ... it's on an incline isn't it?

So not the whole weight will pull against the spring.
 
  • #13
so would it be (cos 65)(2.0)? since its on the horizontal X axis?
 
  • #15
kiarrahannice said:
so would it be (cos 65)(2.0)? since its on the horizontal X axis?

Actually if you look at the link I provided you will see that it is Sin65 that you want. But again you want sin 65 of 2*9.8 the weight.
 
  • #16
I was looking for how to solve the equation You are confusing me. Thanks for your help anyways
 
  • #17
kiarrahannice said:
I was looking for how to solve the equation You are confusing me. Thanks for your help anyways

Before you can solve an equation you have to be able to write it.

Just giving you the equation isn't going to help you learn the material.

Besides that would be against the spirit of the general forum guidelines.
 
  • #18
no it wouldn't people do it all the time within the physics forum. I have LEARNED so much by individuals writing the steps out including when my professor writes the equation for our class. It's okay if you choose to be difficult I will just ask someone else who is willing to help and so I can learn by example instead of toying with me. Again thanks. We just uphold to different styles of learning, and I can respect ur's and in the "spirit of general forum" Please respect mine and others who learn the same way.
 

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