A) lifting the 50-kg sack
B) lifting the 25-kg sack
C) Both require the same amount of work
U1 = m1gh1 = 50*9.8*2 = 980 joule
U2 = m2gh2 = 25*9.8*4 = 980 joule
C) Both require the same amount of work
Scientifically, (C) the amount of work is the same. However, practically, the answer is probably (B) lifting the 25 Kg sack because you very likely will not be able to get the 50 Kg (110 pound) sack off of the ground by yourself unless you are either a gorilla or a former Governor of California.
depends on the (accuracy) of the assumptions made. Only if uniform gravitational field assumed can it be C.
"true" answer depends on how the gravitational field varies with height, and if you're bothered with the tiny differences such variations would cause over 2m
the attractive forces of gravity simply aren't constant. It obeys inverse square laws. ie it can be modelled as F=G*m1*m2/distance^2
In general as you get higher up from the Earth the smaller the attractive forces of gravity is because there's more distance between the object and the Earth). There's also the case that to "hover" above a point, requires a greater rotational speed (for object to stay fixed above a point) That means there more "centrifugal" force in effect countering gravity,In such case it's would be a tiny bit less work to lift the 25kg sack 4 meters.
similarly gravitational field strength is (usually) less down the bottom of deep mines(the earth above pulls up), than on the surface. If lifting at the bottom of mine shaft, if would be easier to lift the 50kg sack the 2m.
--edit
if this is a school question your teacher will almost certainly be expecting C!
If you are able/willing to debate the issue maybe see what happens if non uniformity of gravitational fields is to be considered ;-)
C
Work= Force x Displacement
= m x g x h
Case 1-
Work= 50 x 9.81 x (-2)
= -981kW
Case 2
work= 25 x 9.81 x (-4)
= -981kW
The minus sign denotes negative displacement and Work done by the system.
C
Help Please
A) lifting the 50-kg sack
B) lifting the 25-kg sack
C) Both require the same amount of work
