Velocity ratio of a third class lever

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Homework Help Overview

The discussion revolves around the calculation of the velocity ratio (VR) of a third class lever, where the distances from the load to the effort and from the effort to the pivot are provided. The original poster presents a scenario involving specific load and effort values, along with an initial calculation of mechanical advantage (MA) and an attempt to derive the velocity ratio using vertical distances.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants discuss the relationship between mechanical advantage and velocity ratio, questioning the correct application of vertical distances in the calculations. Some suggest using the geometry of similar triangles to visualize the problem, while others express uncertainty about the definitions of the ratios and their implications.

Discussion Status

There is ongoing exploration of the concepts involved, with some participants offering guidance on using geometric reasoning. Multiple interpretations of the velocity ratio are being considered, particularly in relation to mechanical advantage and efficiency. No consensus has been reached, and participants continue to seek clarification on the calculations.

Contextual Notes

Participants mention constraints such as the requirement to use vertical distances and the implications of efficiency on the calculations. There is also confusion regarding the definitions of velocity ratio and mechanical advantage, particularly in the context of a third class lever.

rad10k
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Homework Statement



3rd class lever 5m distance from load to effort and 1m distance from effort to pivot.

Load = 1962

Effort required to lift load = 11772N

MA = 0.16 or 1/6 ( so there really is no MA)

Calculate the velocity ratio of the system ?

Homework Equations



I have been told to use vertical distance to solve but I don't know how to work ouyt the vertical distance

VR = Distance moved by effort / distance moved by load




The Attempt at a Solution



My attempt was

1 / 6 = 0.167777 or 0.17

I have been told this is wrong and I must use the vertical distance but I can't find anywhere that will help me work this out can someone offer me guidance please.
 
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That looks correct to me. You can find the ratio using the geometry of similar triangles ( draw a sketch)...if the load end moves up 1 m, the effort point moves up by 1/6 m, during that same time period. You can assume any distance you want...the ratio will be the same for vertical distance or velocity.
 
thanks
 
rad10k said:

Homework Statement



3rd class lever 5m distance from load to effort and 1m distance from effort to pivot.

Load = 1962

Effort required to lift load = 11772N

MA = 0.16 or 1/6 ( so there really is no MA)

Calculate the velocity ratio of the system ?

Homework Equations



I have been told to use vertical distance to solve but I don't know how to work ouyt the vertical distance

VR = Distance moved by effort / distance moved by load

The Attempt at a Solution



My attempt was

1 / 6 = 0.167777 or 0.17

I have been told this is wrong and I must use the vertical distance but I can't find anywhere that will help me work this out can someone offer me guidance please.

Homework Statement


Homework Equations


The Attempt at a Solution


PhanthomJay said:
That looks correct to me. You can find the ratio using the geometry of similar triangles ( draw a sketch)...if the load end moves up 1 m, the effort point moves up by 1/6 m, during that same time period. You can assume any distance you want...the ratio will be the same for vertical distance or velocity.

Since it's the load which moves at a greater velocity (It moves a greater distance in a given time.), the velocity ratio is:

{{v_{Load}}\over{v_{Effort}}}={{6}\over{1}}\ .

 
SammyS said:

Since it's the load which moves at a greater velocity (It moves a greater distance in a given time.), the velocity ratio is:

{{v_{Load}}\over{v_{Effort}}}={{6}\over{1}}\ .

But the VR is Veffort/Vload = 1/6.
 
PhanthomJay said:
But the VR is Veffort/Vload = 1/6.

If I did that wrong, I apologize.

I was thinking that since Mechanical Advantage is:

\displaystyle \text{MA}={{F_{Load}}\over{F_{effort}}}\,,

then velocity ratio would be similar.
 
I wasn't sure of the ratio either, which was the numerator and which was the denominator? I gather for a third class lever, where you have to apply a large force to lift a small load, the MA is less than 1, sacrificed to get a higher load velocity.
 
yes the MA is 1/6 which I am dividing 1 by 6 to get 0.17(0.167777) to us in the VR formula



Assuming 100% efficiency , if the energy put in was 3000j would I be correct in think that
the output energy would also be 3000J since ouput = input/efficiency ie. 3000J/100*100 = 3000J ?

Then the next question relating is : If the efficiency of the system is 65% , calculate the Velocity ratio?

The formula I am using for this is : VR = MA/efficency

so, VR 0.17/65*100 = 0.26

Although that is more than I started with so I think how can that be correct?

Thanks for any help
 
Efficiency is output/input.
 
  • #10
Hi, I'm stuck on the same question.

The velocity ratio seems at first glance to be 1/6 as the load is 6 times further from the fulcrum than the effort though in the next question it states the efficiency is 65% giving a vr of 0.256?
 

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