Finding Spring Constant Question

[mohabitar]

For number 3, I'm trying to find that spring constant. We know that k=mg/x. So it should be 9.5(9.8)/.13, which is incorrect. However since it is on an incline, we should find the incline aspect of gravity, which I found to be 3.5, but that didnt work either. I've tried a lot of different values, none seem to work. Any hints?

 

[PhanthomJay]

You've got to include the component of gravity acting down the plane, friction up the plane, and the spring force. Please show how you arrived at your solution.

 

[mohabitar]

Well I haven't really arrived at a solution. I was just playing with numbers and plugging them in the system until I got a green checkmark, but that's not really what I should be doing. Am I using the right equation, k=mg/x? And for m I'd use 9.5 and for g, I'd have to find the incline aspect of gravity using trig, and for x id just use .13? That should give me the answer I'm looking for or is there more?

 

[PhanthomJay]

You can't just be checking boxes until a green checkmark shows up. You've got to understand the basic concepts of vectors, friction, forces, Newton's laws, free body diagrams, etc. You might want to start by showing us your method for the solution of the 2nd problem. Read up in your text on incline planes , or search on-line.

 

[mohabitar]

For the second problem, I used a formula that was discussed in a pre-lecture video example: a=9.8(u[k]cosx-sinx), x being theta and u[k] being the coefficient of friction. Not really sure how that formula works, but it got me the right answer. I really want to understand this stuff rather than just plug in numbers into formulas, but there's just so much work to do in this class where it doesn't give me much time to spend some quality time on each problem, so I am left with just doing everything as quickly as possible :(