physics

[amar21]

A 6 ft man lifts a 100-lb weight from the floor to a height 1 ft above his head.

What force must be exerted by the man to sustain the object above his head?

Answer: 100lb force

NEVERMIND! i just figured it out... before I was figuring out why we didnt include the acceleration of gravity in calculating force

F = mg, mg = W ...

Fup = Fdown where Fnet =0 ... So... Fup=mg, Fup=W, Fup= 100

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[talkalot24]

I still don't follow.

W= mg = 100 * 10 = 1000 ???

 

[Soccerdoc11]

Lbs is a unit of Weight (Force) which already takes in account gravity

 

[Vihsadas]

That's right!
For everyone else who might be reading, be careful to differentiate between lbs and Kg. We often take them interchangably in normal life because they differ only by some factor of gravity. But we have to remember that gravity has units associated with it, so the difference between lbs and Kg isn't just a numerical difference. It's a difference in the units too. One is a unit of mass (Kg) and one is a unit of force (lbs).

 

[pyromatic]

-------- SI <--------> English
Mass: gram <-------> slug (no joke)
Force: newton <-----> pound

1 lb = (1 slug)*(1 ft/s^2) which is analogous to 1 N = (1 kg)*(1 m/s^2)