Chemistry Reference
In-Depth Information
EXAMPLE A.8
What is the cost of 14.0 oz of hamburger if the store charges $3.20 per pound?
Solution
Do not
simply multiply:
45.5 oz
#
dollar
lb
a
3.25 dollars
1 lb
14.0 oz
b
Instead, first convert one of the quantities to a unit that matches that of the other
quantity:
a
1 lb
16 oz
14.0 oz
b
0.875 lb
a
3.20 dollars
1 lb
0.875 lb
b
2.80 dollars
The same principles apply to the metric units used in science.
EXAMPLE A.9
A car accelerates from 0.0 mph to 45.0 mph in 5.00 s. What is the acceleration
of the car? (Acceleration is the change in velocity per unit of time.)
Solution
The change in velocity is
45.0 miles/hour
0.0 miles/hour
45.0 miles/hour
45.0 miles/hour
5.00 s
9.00 miles/hour
s
The acceleration is 9.00 miles per hour per second. [This is an example of one
of the few times when two different units may be used for the same quantity
(time) in one value (the acceleration).]
Practice Problem A.9
A sprinter accelerates from 0.00 m/s to 13.5 m/s
in 0.300 s. What is his acceleration?
Percentage
The percentage of a certain class of items within a whole group is equal to
100% times the number of items in the group divided by the number in the
entire group. For example, the percentage of men within a class having 16 men
and 80 students total is
16 men
80 students
100%
a
b
20% men
