Energy and friction -- Can the block make it all the way up the ramp?

[LulyPop]

Homework Statement

Can the block go up the ramp completely even with the friction of the ramp?

Relevant Equations

∆E = ∆K - ∆U
∆U = m* g* h
Wm = -1/2 kx²
Wfat = µc * m *g *d

 

[BvU]

Hello @LulyPop,

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Please try again: provide a full problem statement instead of repeating a set of (relevant) equations. And include the figure mentioned ...

https://www.physicsforums.com/threads/homework-help-guidelines-for-students-and-helpers.686781/

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[Dr.D]

There will be an impact event when the block reaches lower end of the ramp. Do you wish to correctly consider that and the associated energy loss, or did you intend this to be done assuming energy is conserved until the friction work on the ramp occurs?

 

[LulyPop]

There will be an impact event when the block reaches lower end of the ramp. Do you wish to correctly consider that and the associated energy loss, or did you intend this to be done assuming energy is conserved until the friction work on the ramp occurs?

Hi!
I didn't think about the impact with the start of the ramp. I considered that until we go up the ramp we have only conservative forces. When going up, as we have the kinetic frictional force, which is a non-conservative force, I think it reduces the speed of the block and transforms the kinetic energy of the block to another form of energy.

 

[berkeman]

Hi!
I didn't think about the impact with the start of the ramp. I considered that until we go up the ramp we have only conservative forces. When going up, as we have the kinetic frictional force, which is a non-conservative force, I think it reduces the speed of the block and transforms the kinetic energy of the block to another form of energy.

Yeah, I think this is a simple enough problem (as shown) that you don't need to consider the abrupt transition impact. Just go ahead and solve it using the friction coefficient (and associated force) changing the PE-KE balance. Please show us your work. Thank you.

 

[LulyPop]

Yeah, I think this is a simple enough problem (as shown) that you don't need to consider the abrupt transition impact. Just go ahead and solve it using the friction coefficient (and associated force) changing the PE-KE balance. Please show us your work. Thank you.

Thank you for the tips. I'll try again!

 

[Dr.D]

It is a pretty good assume conservation of energy as the block approaches the ramp. However, the impact at the sudden direction change will reduce the kinetic energy available for the climb.

 

[BvU]

Don't we need some initial condition ? I feel it makes a difference if the spring is compressed by 2 m instead of 0.5 m ...
Or is that part of the exercise ?

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[LulyPop]

Don't we need some initial condition ? I feel it makes a difference if the spring is compressed by 2 m instead of 0.5 m ...
Or is that part of the exercise ?

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Exactly! I tried it in several ways and got the x of the Elastic Potential Energy formula (U = kx ^ 2/2). Today the professor said he was wrong and added a piece of information to the question. He forgot to say that x = 20cm

 

[LulyPop]

It is a pretty good assume conservation of energy as the block approaches the ramp. However, the impact at the sudden direction change will reduce the kinetic energy available for the climb.

I am dividing the problem into two parts. And I will follow your line of reasoning. Thank you very much!

 

[BvU]

I am dividing the problem into two parts. And I will follow your line of reasoning. Thank you very much!

To get started, don't make things too difficult.
You have initial spring compression energy $\rightarrow$ initial kinetic energy $\rightarrow$ maximum $\Delta h$.
So the yes/no can be resolved. Since you know nothing about the sudden direction change, the best you can do is assume that speed changes direction, not magnitude at that point.

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