Heat and work. Fit ring over rod, remove ring from rod

[nicoleb14]

It is desired to slip an aluminum ring over a steel bar. At 7.00° C the inside diameter of the ring is 4.000 cm and the diameter of the rod is 4.080 cm.

(b) Find the temperature of the ring at which it fits over the bar. The bar remains at 7.00° C.
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It is desired to slip an aluminum ring over a steel bar. At 21° C the inside diameter of a ring is 4.000 cm and the diameter of a rod is 4.004 cm. By heating the ring, it expands so that it can slip over the bar, after which time they both are allowed to cool to the same temperature, so that the ring is now stuck on the bar.

(b) Find the temperature at which the ring can be removed. Express your answer to the nearest whole degree.


Attempt:
i don't know even know where to start.
i tried (kAdeltaT)/L
but i don't know what A is!

 

[Doc Al]

i don't know even know where to start.
i tried (kAdeltaT)/L
but i don't know what A is!

What's the formula describing linear thermal expansion? ΔL/L = ?

You should be able to look up the expansion coefficients for aluminum and steel in your text.