A machinist needs to remove a tight-fitting pin of material A from a hole in a block made of material B. The machinist heats both the pin and the block to the same high temperature and removes the pin easily. What statement relates the coefficient of thermal expansion of material A to that of material B? a. The situation is not possible, heating block B will shrink the hole in the material as the material expands with increasing temperature
b. Material B has the same coefficient of expansion as does material A
c. Material B has a negative coefficient of expansion and A has a positive coefficient of expansion
d. Material A has a greater coefficient of expansion than does material B
e. Material B has a greater coefficient of expansion than does material A

C. Material B has a negative coefficient of expansion and A has a positive coefficient of expansion

Explanation:

If both material A and material B have the same coefficient of thermal expansion and they were heated to same temperature, both will expand making it impossible to remove the pin from the hole.

Also, if the coefficient of thermal expansion of any of the materials is higher than the other and they were subjected to the same temperature, the material with lower coefficient of thermal expansion will expand, making it impossible to remove the pin.

However, materials with negative coefficient of thermal expansion will contract on heating instead of expanding, while materials with positive  coefficient of expansion will expand on heating. This makes it possible to remove the pin from the hole in the block.

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explanation:

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a and c

c is 100% but i am confused in a