# physics

Discussion in 'MCAT Study Question Q&A' started by amar21, May 30, 2008.

1. ### amar21 professional crammer 7+ Year Member

Joined:
Feb 27, 2006
Messages:
235
0
Status:
Pre-Medical
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?

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

2. ### talkalot24 Member 10+ Year Member

Joined:
Jul 21, 2004
Messages:
169
0
Status:
Medical Student
I still don't follow.

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

3. ### Soccerdoc11 2+ Year Member

Joined:
Apr 9, 2008
Messages:
195
0
MDApps:
Status:
Pre-Medical
Lbs is a unit of Weight (Force) which already takes in account gravity

Stop hovering to collapse... Click to collapse... Hover to expand... Click to expand...
4. ### Vihsadas No summer Moderator EmeritusLifetime DonorClassifieds Approved 5+ Year Member

Joined:
Oct 17, 2007
Messages:
5,472
53
Status:
Medical Student
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).

Stop hovering to collapse... Click to collapse... Hover to expand... Click to expand...

Joined:
Jul 17, 2006
Messages:
38