Math Is Fun Forum

Kurtz

Member

Registered: 2007-10-01

Posts: 27

First Law of Thermodynamics

A 150 kg steel rod in a building under construction supports a load of 6050 kg. During the day, the rod's temperature increases from 22 degree celsius to 47 degree celsius. This temperature increase causes the rod to thermally expand and raise the laod 5.5 mm.

a. Find the energy transferred as heat to or from the rod.(Hint: Assume the specific heat capacity of steel is the same as for iron.)

b. Find the work done in this process. Is work done on or by the rod?

c. How great if the change in the rod's internal energy? Does the rod's internal energy increase or decrease?

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JaneFairfax

Member

Registered: 2007-02-23

Posts: 6,868

Re: First Law of Thermodynamics

(a) Multiply the specific heat capacity of steel by the mass of the rod and the difference in temperature.

(b) The work done by the rod on the load is equal to the change in the gravitational potential energy of the load (i.e. weight of load times vertical displacement).

(c) Use the first law of thermodynamics (change in internal energy of rod equals heat supplied to rod minus work done by rod).