laczlacylaci

2+ Year Member
Jun 20, 2016
264
45
Cheese State
Status
Pre-Medical
upload_2016-8-31_9-59-7.png
P=W/t (J/s)
J/s=(N*m)/s=kg*m^2/s^3, so A is the answer.

C=(ft*lb)/s
ft-measure of length, kind of like m
lb-measure of weight, kind of like kg
s-stays the same.
So this would equal to about (m*kg)/s, why is this an expression of power? kg*m is not J.
 

theonlytycrane

5+ Year Member
Mar 23, 2014
1,956
1,687
Status
Medical Student
kg is a unit of mass but lb is a unit of weight (a force). So it's like length * force / time.

When doing this one I didn't want to think about (C) so I just eliminated (B)/(D) and was happy when I figured out (A) was wrong.
 
  • Like
Reactions: laczlacylaci

TheLongGame

2+ Year Member
Sep 4, 2016
68
49
Status
Medical Student
ImageUploadedBySDN1473459848.102050.jpg

There is a difference between pound mass [lbm] and pound force [lbf]. Unfortunately this question didn't specify which one it was, but it was easy to determine which form of the generic "lb" they meant once you crunch the units.

If "A" had been a unit of power, then your only option left would be to assume that the testers gave you lbm in option C, which would be in momentum units and therefore the correct answer.

Oh, and I forgot to define the relationship between pound mass and pound force

lbf=lbm*(ft/s^-2)

Momentum: Kg*m/s = N*s , lbm*ft/s = lbf*s


Sent from my iPhone using SDN mobile
 
Last edited:
  • Like
Reactions: AquaticSunrise13