A nurse holding a newborn 3.0-kg baby at a height of 1.2 m off the floor carries the baby 15 m at constant velocity along a hospital corridor. How much work has the force of gravity done on the baby?

Question

anonymous · Answer

m = 3 kg
h = 1.2 m
delta d = 15 m
g = 9.8 N/kg
Fg = ?

F = Fg = mg
           = (3 kg)(9.8 N/kg)
           = 29.4 N

amistre64 · Answer

how far has the baby moved in the direction of gravity?

anonymous · Answer

zero.

amistre64 · Answer

then by all accounts; gravity hasnt done any work

anonymous · Answer

ohh..

anonymous · Answer

how do I know whether work is zero, and if gravity hasn't done any work?

amistre64 · Answer

gravity moves things in one direction; down.  if there is no distance moved doward, no work is done in that direction

anonymous · Answer

ohhh.. thank you!

amistre64 · Answer

if the nurse lifts the baby; then work is done against gravity

anonymous · Answer

oh but in this case it was asking how much work has the force of gravity done on the baby..

anonymous · Answer

does lifting the baby a part of the question?

amistre64 · Answer

lifting is not mention in the question; but say the question says:

how much work is done to life the baby up to 1.5 meters

then we do the W = F*d stuff

amistre64 · Answer

3 kg * 1.5 m = 4.5 kg/m  of work

anonymous · Answer

ohhh.. okay, thank you! :)