The load of an object on a pivot

[simonwait]

Hi

I have a 3.2m platform which weighs 175Kg. One end of the platform is touching the floor but the other end is on a pivoting bolt 2.5m in the air.

I need to figure out what the "load" would be on the end which is on the floor when I try to lift that end 4.5m in the air. Basically so I can spec a winch or hoist to lift it.

 

[haruspex]

Hi

I have a 3.2m platform which weighs 175Kg. One end of the platform is touching the floor but the other end is on a pivoting bolt 2.5m in the air.

I need to figure out what the "load" would be on the end which is on the floor when I try to lift that end 4.5m in the air. Basically so I can spec a winch or hoist to lift it.

Do you mean, what force is required to lift it at the free end?
It depends on the angle at which you apply the force. If you pull straight up, it will be half the weight of theplatform, regardless of the platform angle.
If you pull at right angles to the platform it will be less at first but will increase until the platform is level. At that point it will once again be half the weight of the platform. After that it will reduce again.

 

[simonwait]

OK great.

Yeah meant lifting the free end

Because of how it moves as its lifted then i would expect about 2 degrees either side of a direct lift vertically but based on it therefore not being far off then i will assume 1/2 the weight which is well within the limits of the winch I am looking at with an SWL of 125kg.

Thanks for your help

 

[haruspex]

OK great.

Yeah meant lifting the free end

Because of how it moves as its lifted then i would expect about 2 degrees either side of a direct lift vertically but based on it therefore not being far off then i will assume 1/2 the weight which is well within the limits of the winch I am looking at with an SWL of 125kg.

Thanks for your help

Wait a moment...
With the lengths you quoted, you might have trouble keeping the cable within a few degrees of vertical. How high is the top of the cable?

 

[simonwait]

When the platform is down the cable is paid out about 14m from the drop point

Its also about 250mm further away from the pivot than the end of the platform so there is about of an arc.

 

[haruspex]

Its also about 250mm further away from the pivot than the end of the platform

Is that when the platform is resting on the ground or when it is horizontal?

 

[simonwait]

When its on the ground

 

[haruspex]

When its on the ground

Ok.
In general, finding the max load on the cable is quite a tricky optimisation problem, but with that 14m height I think you are ok.

 

[sophiecentaur]

It may be worth while doing a scale drawing (for both conditions) and checking that the angles are near enough 90 degrees. (If you don't want to get involved with the Trig.) If the angle gets as low as 80 degrees, there's only a couple of percent of difference. 45 degrees will only make a force 40% more.
Btw, has it been established that the platform is uniform? Also, what will be on the platform? With that weight be significant?