Chemistry Reference
In-Depth Information
Alternatively,
Definition
of hour
Definition
of minute
Hours
Minutes
Seconds
(
)
= 310.5 minutes
(
)
60 minutes
1 hour
60 seconds
1 minute
5.175 hours
= 18,630 seconds
or
(
)
(
)
60 seconds
1 minute
60 minutes
1 hour
= 18,630 seconds
5.175 hours
In this particular problem, it does not matter if we press the equal key on the
calculator after entering the first 60. Similarly, we can write down the 310.5 min
or not write it down, as we please, but the final answer is still the same.
Practice Problem 2.5
Calculate the number of seconds in exactly 7
weeks.
A factor can be raised to a power if the units to be converted require that.
Remember that when a ratio in parentheses is raised to a power,
all the num-
bers
and
all the units
within the parentheses must be raised to that power.
EXAMPLE 2.6
(ft
2
)
(yd
2
)
How many square feet
are in 12.0 square yards
?
Solution
b
2
a
3 ft
1 yd
12.0 yd
2
Square
yards
Square
of factor
Square
feet
a
9 ft
2
1 yd
2
12.0 yd
2
108 ft
2
b
The second factor can be derived as follows:
3 ft
1 yd
(3 ft)
2
(1 yd)
2
3
2
ft
2
1
2
yd
2
9 ft
2
1 yd
2
Note that the number 3 is squared, the unit
feet
is squared, the number 1 is
squared, and the unit
yard
is squared. There are
9 ft
2
yd
2
in 1
(Figure 2.3).
(ft
3
)
Practice Problem 2.6
How many cubic feet
of cement can be
(yd
3
)
held in a cement mixer with a capacity of 7.34 cubic yards
?
