Question

A large steel wheel is to be fitted on to a shaft of the same material. At 27°C, the outer diameter of the shaft is 8.70 cm and the diameter of the central **** in the wheel is 8.69 cm. The shaft is cooled using 'dry ice'. At what temperature of the shaft does the wheel slip on the shaft? Assume coefficient of linear expansion of the steel to be constant over the required temperature range:

αsteel = 1.20 x 10-5 K-1

Answer 1

Given αsteel = 1.20 x 10-5 K-1 (coefficient of lin. exp. of steel)

T1 = 27°C = 27 + 273 K = 300 K

Length at temperature, T1K = lT1 = 8.70 cm

Length at temperature, T2K = lT2 = 8.69 cm

Change in length = lT2 - lT1 = lT1 α(T2 - T1)

⇒ 8.69 - 8.70 = 8.70 x (1.20 x 10-5) x (T2 - 300)

⇒ T2 - 300 = {0.01}/{8.70 x 1.2 x 105} = -95.8

T2 = 300 - 95.8 = 204.2 K

= -68.8°C