power required to lift a mass

[turbinef14]

how do i calculate the motor required to lift a mass
eg mass = 75kg what hp is required

 

[sreid]

75 kg = 165 lb

1 m/s = 3.3 ft/sec

Power = 165 x 3.3 = 541 lb-ft/sec

550 lb-ft/sec = 1 HP

541/550 = approx 1 HP

 

[Skogsgurra]

Since everyone seems to have had a go on this...

"Our" (European) definition of one horsepower is "The power needed to lift a mass of 75 kg vertically 1 m in 1 second"

This is suspiciously similar to the OP that says that he needs to lift 75 kg at a speed equal to 1 m/s.

Using SI, we get: P = 75*9.8065*1 = 736 W (the European HP).

The efficiency stated is 0.7, so you would need something like 1050 watts.

Then, there are lots of other things to consider. But your original question has this answer.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[cswilson]

This is reminding me of a junior high physics lesson I got, way back when. The teacher was trying to make the concept of power real to us. In the lesson, each of us had to be weighed, then be timed in the 50-yard dash. From that we were supposed to calculate the power we could each generate.

In approximate numbers, I weighed 100 pounds then, and I ran 50 yards in 8 seconds. So I was supposed to calculate:

100lbs * 150ft / 8sec = 1875lb-ft/sec

1875lb-ft/sec * 1HP/(550lb-ft/sec) =3.41HP

Now this bothered me -- I knew that a horsepower was in some sense the power that a horse could generate. As a scrawny little 12-year old, it didn't seem to me that I could generate more power than 3 horses.

But it turned out to be a great "life lesson". It got me started on really understanding the difference between mass and weight. (This has saved me a lot of grief in moment-of-inertia calculations.) More importantly, it got me verifying and double-checking the information supposedly knowledgeable people gave me. I realized that if I wanted really to understand things, I was going to have to build up my own knowledge from first principles. Even on this forum, I've seen people [mis]use "plug-and-chug" formulas without understanding what goes into them.

Curt Wilson
Delta Tau Data Systems

 

[GregLocock]

Well no wonder you were confused. He was assuming that the resistance to motion, horizontally, equalled your weight.



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[electricpete]

You're so picky Greg, worrying about minor details like physics all the time.

I mean really...how much harder could it possibly be to run vertically up a ladder at 6 yards/sec than it is to run accross a sidewalk at 6 yards/second!

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[electricpete]

I hope no one was offended by my moment of giddyness.

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[GregLocock]

We did a similar experiment at school, running up a flight of stairs. Fit fat rugby players did manage around 1 hp of vertical PE gain.

Incidentally (and obviously) a horse can produce far more than 1 hp, but on average over a day that is about what you'll get. wiki says 15 hp, briefly



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[aolalde]

By definition:
1 HP = 33000 LB x FT/1 min

75 Kg = 165.35 Lb
1 m/s = 196.85 Ft/min
Eff = 0.75
Your power requirement:

P = 165.4*190.85/(0.75*33000) = 1.315 HP = 0.981 kW

 

[Skogsgurra]

...or, using the OP's efficiency: 1051 watts.

Which is something you arrive at with no other constants and factors than g, if you use SI.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...