Mistakes in answers to Practice Exercises in Ch 1

[Zellmer, Robert]

A fellow student pointed out there were some errors in some of the answers
to the Practice Exercises which come at the end of a Sample Exercise.
Hopefully, you're trying the Sample Exercises and the Practice Exercise
that follows and then the Self Assessment questions as you're analyzing
the material (reading for content and understanding).

Here's the mistakes and the correct answers.

Practice Ex 1.3

The answer for degF is correct but has incorrect s.f.  The 260 K should technically
have only 2 s.f. since you shouldn't consider the zero as significant written like
this or given specific knowledge.  However, usually for temps written this way the
zero in the units place is taken as sig.  That's because when measuring temps to
estimate to the units place the thermometer would be marked only in the tens
place (10, 20, 30, etc.).  Thermometers are usually more accurate than that
(marked at least to the units place).

So, assuming the 260 K has 3 s.f. and is known to the units place when you get
degC you get,

260-273.15 = -13.15 C = -13 C, to the units place, 2 s.f.

Then convert to degF,

degF = (9/5) (-13.15 C) + 32 F = (-23.67 F + 32 F) = 8.33 F = 8 F, to the units place.

Practice Ex 1.8

The question simply asks if the density of the gas can be calculated to 4 s.f. if the masses
in Figure 1.25 are to 3 decimal places.  That does give an extra s.f. to the mass of the gas
(4 s.f.) but the volume (1.05 x 10^3 cm^3) has only 3 s.f. so the density still has only 3 s.f.

So, the answer is simply NO but the answer given is 9.52 m/s.

Practice Ex 1.9

The answer to this one is the answer to P.E. 1.8.

The answer should be 2.0376 x 10^-4 and should be rounded to 3 s.f.

The addition rule must be used first for the denominator.  That means both
numbers must be to the same power of ten.  It doesn't matter which power of
10 you chose.

4.3 x 10^4  +  67.5 x 10^4.  Now that they're both to the same power of 10
we see they're both known to the 1st decimal place.  The answer of 71.8 x 10^4
is known to the 1st decimal place and has 3 s.f.  Then do the division and use
the mult/div rule.

146.3/(71.8 x 10^4) = 2.03760 x 10^-4.  This must be rounded to 3 s.f.
Thus, the answer is 2.04 x 10^-4 (3 s.f.).

Practice Ex 1.10

The answer given is 2.04 x 10^-4 w/o a unit.  This is the answer to PE 1.9.

It should be 804.672 km and rounded to 4 s.f., 804.7 km since the original
distance is 500.0 mi (4 s.f.).

Practice Ex 1.11

The books answer is 804.7 km.  Lo and behold, this is the answer to 1.10.
The correct answer should be 13.6046 km/L which is 14 km/L to 2 s.f.

Practice Ex 1.12

The books answer is 12 km/L.  The answer should be 3.7558 km which
is 1.232 x 10^4 ft which rounds to 1.2 x 10^4 ft.

Practice Ex 1.13

The books answer is 1.2 x 10^4 ft.  Yep, the answer to PE 1.12.

The answer should be 831.834 g which is 832 g.  It should have 3 s.f.

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