Spring with a mass at an angle, need original length of spring

AI Thread Summary
The discussion centers on calculating the unstretched length of a spring attached to a 5 kg mass on a 45-degree incline. The user initially calculates the forces acting on the mass and determines the spring's force using Hooke's law, leading to a conclusion that the unstretched length of the spring appears to be negative, which is nonsensical. The user suspects there may be an error in the problem setup or the spring constant value. Despite drawing a free body diagram to analyze the forces, confusion persists regarding the calculations and the physical feasibility of the results. The thread highlights the importance of verifying problem parameters and calculations in physics homework.
2Dark4u
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Homework Statement



The Setup is depicted in the Attachment. Essentially there is a 5kg Mass on an incline (45). The incline measures 0.4m from the mass to the corner were it turns 90 degrees and measures 0.3m to were there is a spring (k = 20N/m. This spring attaches to the Mass. This system is in equilibrium with the spring stretched out as it is.

The question is what is the length of the Spring not stretched. As in if the mass was un attached and the spring was at rest?

Homework Equations


Only relevant equation i can think of is F = k(λx) Basic Hookes law

The Attempt at a Solution



So first thing I did
5* 9.8 = 49N

Then 49cos(45) to get Fx of mass = 34.65N this should equal the X component of the force of the spring.

Second the spring should measure 0.5 since it makes a triangle right triangle with 0.4 and 0.3 this also means the angle its at in relation to the x component of force is 36.87

so F of the spring should be Fx = F cos(36.87)

34.65N / cos( 36.87) = 43.31N

then F = k λx and F/k = λx

43.31/20 = 2.16m

Now if the spring stretch measures 0.5m I don't see how λx can equal 2.16m

That would mean that the spring has a negative measurement when unstretched and that doesn't make any sense.

So help me out, were did I go wrong.
 

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2Dark4u said:

Homework Statement



The Setup is depicted in the Attachment. Essentially there is a 5kg Mass on an incline (45). The incline measures 0.4m from the mass to the corner were it turns 90 degrees and measures 0.3m to were there is a spring (k = 20N/m. This spring attaches to the Mass. This system is in equilibrium with the spring stretched out as it is.

The question is what is the length of the Spring not stretched. As in if the mass was un attached and the spring was at rest?

Homework Equations


Only relevant equation i can think of is F = k(λx) Basic Hookes law

The Attempt at a Solution



So first thing I did
5* 9.8 = 49N

Then 49cos(45) to get Fx of mass = 34.65N this should equal the X component of the force of the spring.

Second the spring should measure 0.5 since it makes a triangle right triangle with 0.4 and 0.3 this also means the angle its at in relation to the x component of force is 36.87

so F of the spring should be Fx = F cos(36.87)

34.65N / cos( 36.87) = 43.31N

then F = k λx and F/k = λx

43.31/20 = 2.16m

Now if the spring stretch measures 0.5m I don't see how λx can equal 2.16m

That would mean that the spring has a negative measurement when unstretched and that doesn't make any sense.

So help me out, were did I go wrong.

I wonder if k was supposed to equal 20 kN/m
 
correction ! sorry
 
Draw a Free Body Diagram for the 5 kg block.

attachment.php?attachmentid=45157&d=1331882305.jpg
 
Ive checked with everybody. And so far what people have been able to tell me is that it just looks like the question has to be wrong

I did draw the diagram, its how i saw were all the forces were going. Unless I messed it up somehow.
 
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