Worksheet #35 – First Law of
Thermodynamics
Supplemental Instruction
Iowa State University
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Review Questions
Wesley
PHYS 221
Whisnant
04/23/2014
1. (46.2%) A 75-kg man sits in a 40-kg, 3.5 m long boat that is floating on a lake. Initially,
he is at the right end of the boat, which is farthest from the dock (see diagram below).
The man moves to the left end of the boat, intending to get off. How far from the dock
does he end up, in m? Assume the boat floats without friction on the water.
2. (44.1%) What is the center of mass position of the object shown here (xCM, yCM), in m?
The length L is 6.0 m, and the total mass of the object is 6.0 kg. The object has uniform
density.
(79.9%) What is the moment of inertia of the object, in kg-m2, for rotation about an axis
through the right end and perpendicular to the plane of the paper?
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Do NOT plug in numbers until you have solved for the desired variable!
Try to solve each problem algebraically first.
Today’s Exercises
1. (Internal Energy) A gas in a cylinder expands from a volume of V1 to V2 Heat flows into
the gas just rapidly enough to keep the pressure constant at P during the expansion. The
total heat added is Q.
a. Find the work done by the gas.
b. Find the change in internal energy of the gas.
c. Does it matter whether the gas is ideal? Why or why not?
2. (First Law of Thermodynamics) The process shown in the pV-diagram here involves
0.0175 moles of an ideal gas.
a. What was the lowest temperature the gas reached in this process? Where did it
occur?
b. How much work was done by or on the gas from a to b? What about b to c?
c. If 215 J of heat was put into the gas during abc, how many of those joules went
into the gas’s internal energy?