X(3600s/1hr)^2=(1.38013017E+10in/hr^2)Conversion of 9.8m/s^2 to in/hr^2

[wiskeywiz]

Homework Statement

9.8m/s^2= ? in/hr^2

Homework Equations

The Attempt at a Solution

(9.8m/s^2)X(1ft/.3048m)=(9.8ft/.3048s^2)=(32.15223097ft/s^2)X(12in/1ft)=(385.8267717in/s^2)

 

[dynamicsolo]

You're looking good so far. Now take care of the "seconds" in the denominator...

 

[wiskeywiz]

how to do the seconds

can i do (385.8267717in/s^2) X (60s^2/1hr^2) = 1388976.378in/hr^2. this answer is not correct

 

[cristo]

That's because, firstly, there's not 60 seconds in an hour, and secondly, you need to square this number anyway.

Think of it like the units are $$\frac{in}{s^2}=\frac{in}{s\cdot s}$$. Now, there are 3600 seconds in an hour, so replace that in the denominator to give $$\frac{in}{3600^{-2}hr^2}=\frac{3600^2in}{hr^2}$$

 

[dynamicsolo]

can i do (385.8267717in/s^2) X (60s^2/1hr^2) = 1388976.378in/hr^2. this answer is not correct

Cristo is correct. If you aren't fully comfortable with certain conversion factors, you may want to use more steps, as you did correctly with the portion leading from meters to inches:

(385.8267717in/s^2) X [(60 s/1 min)^2] = (385.8267717in/s^2) X (3600s^2/1 min^2) =

(385.8267717 in X (3600)/min^2) =

(385.8267717 in x (3600)/min^2) X [(60 min/1 hr)^2] =

(385.8267717 in x (3600)/min^2) X (3600 min^2/1 hr^2) =

(385.8267717 in x (3600) x (3600)/hr^2), and so on to the result. The number will be quite enormous.

You don't need to try to skip steps when you're not making a familiar calculation: leaving out steps can increase the risk of making a serious mistake.

 

[wiskeywiz]

i got it. i goofed when i tried being slick and figured 3600s^2 = 60^2/hr^2

 

[dynamicsolo]

i got it. i goofed when i tried being slick and figured 3600s^2 = 60^2/hr^2

Everyone does that, including faculty lecturers, who really should know better... It usually ends up saving time (and sometimes embarrassment) to work out more steps when the calculation is unfamiliar, complicated, or subtle, than trying to make leaps in your head...

Good job!