HP 15c - Manual (Page 81)

Section 6: Programming Basics 81
Problems
1. The village of Sonance has installed a 12-o'clock whistle in the
firehouse steeple. The sound level at the firehouse door, 3.2 meters
from the whistle, is 138 decibels. Write a program to find the sound
level at various distances from the whistle.
Use the equation L = L
0
– 20 log (r/r
0
), where: L
0
is the known sound
level (138 db) at a point near the source,
r
0
is the distance of that point from the source (3.2 m), L is the
unknown sound level at a second point, and r is the distance of the
second point from the source in meters.
What is the sound level at 3 km from the source (r = 3 km)?
A possible keystroke sequence is:
|¥ ´bC 3.2 ÷ |o 20 * “ 138
+ |n |¥ taking 15 program lines and 15 bytes of
memory. This problem can be solved in a more general way by
removing the specific values 3.2 and 138 from the program, and
instead recalling the L
0
and r
0
values from storage registers; or by
removing 3.2 and 138 and loading L
0
, r, and r
0
into the stack before
execution: L
0
v r v r
0
.
(Answer: for r = 3 km, L = 78.5606 db.)
2. A "typical large" tomato weighs about 200 grams, of which about
188 g (94%) are water. A tomato grower is trying to produce
tomatoes of lower percentage water. Write a program to calculate the
percent change in water content of a given tomato compared to the
typical tomato. Use a programmed stop to enter the water weight of
the new tomato.
What is the percent change in water content for a 230 g tomato of
which 205 g are water?
A possible keystroke sequence is:
´bÁ .94 v ¦ (enter water weight of new tomato)
v ¦ (enter total weight of new tomato) ÷ |∆
|n taking 11 program lines and 11 bytes of memory.
(Answer: for the 230 g tomato above, the percent change in percent
water weight is -5.1804%.)