Expansion of an aluminum support column under heart

[imatreyu]

Homework Statement

OMG, Embarrassing typo ^ *HEAT not HEART. :) Sorry! In any case,

A construction worker uses a steel tape to measure the length of an aluminum support column. If the measured length is 18.6 m when the temperature is 21.2 C, what ist he length when the temperature rises to 29.4 degrees C? (Note: Do not neglect the expansion of the steel tape.)

Homework Equations

change in L= $$\alpha$$* Lo * change in T

The Attempt at a Solution

I found the changes in length of both the steel and aluminum, but I don't understand the Note. Why is that important? How does the expansion of the steel tape have anything to do with the expansion of the alumnium support column?

 

[NobodySpecial]

Because you don't know the length of the column - you only know the length of the tape

( The tape changes length as well )

 

[imatreyu]

So 18.7 m is the length of the tape.
So do I find the expansion of the tape and then subtract the expansion of the "column"?
Or vice versa?

 

[NobodySpecial]

Yes or you could re-write the equation in terms of the difference in the expansivities.

- make sure you get the sign right! do you expect the expansion of the tape to make the measured expansion bigger or smaller.

 

[imatreyu]

Okay. :)

Thank you so much!