AAMC Scored C/P #59

[laczlacylaci]

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.

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[theonlytycrane]

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.

 

[TheLongGame]

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


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