Physics HELP!!! 20 點 Thx
2012-11-17 1:45 am
Steel train rails are laid in 12.0-m-long segments placed end to end. The rails are laid on a winter day when their temperature is -2.0 oC. If the rails are originally laid in contact, what is the stress in them on a summer day when their temperature is 33.0 oC?
回答 (2)
2012-11-17 3:09 am
✔ 最佳答案
(delta L)/L = alpha (delta T)Stress=Young Modulus * Strain
Strain=(delta L) / L
You can first find out Strain, Then you can find out Stress.
2012-11-17 8:27 am
The coefficient of linear expansion of steel is 13 x 10^-6 K^-1
Hence, expansion of a rail = 12 x (13 x 10^-6) x (33 +2) m
Strain experienced by the rail at 33'C = [12 x (13 x 10^-6) x 35]/12
= 4.55 x 10^-4
Take the Young's Modulus for steel to be 180 x 10^9 N/m^2
Thus, stress at 33'C = 180 x 10^9 x 4.55x10^-4 N/m^2 = 8.19 x 10^7 N/m^2
Hence, expansion of a rail = 12 x (13 x 10^-6) x (33 +2) m
Strain experienced by the rail at 33'C = [12 x (13 x 10^-6) x 35]/12
= 4.55 x 10^-4
Take the Young's Modulus for steel to be 180 x 10^9 N/m^2
Thus, stress at 33'C = 180 x 10^9 x 4.55x10^-4 N/m^2 = 8.19 x 10^7 N/m^2
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