created 08/01/99; edited 06/09/2015

# Chapter 13 Programming Exercises

## Exercise 1 — Annual Appliance Cost

Write a program that calculates the annual cost of running an appliance. The
program asks the user for the cost per kilowatt-hour and the number of kilowatt-hours
the appliance uses in a year:

Enter cost per kilowatt-hour in cents
8.42
Enter kilowatt-hours used per year
653
Annual cost: 54.9826

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## Exercise 2 — Distance a Brick Travels

When a brick is dropped from a tower, it falls
faster and faster until it hits the earth.
The distance it travels is given by

d = (1/2)gt^{2}

Here d is in feet, t is the time in seconds,
and g is 32.174.
Write a program that asks the user for the number of seconds and
then prints out the distance traveled.

Enter the number of seconds: 5.4
Distance: 469.096

Use the program to determine how far a brick falls in 100 seconds.

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## Exercise 3 — Logarithm Base Two

The base 2 logarithm of a number is defined by:

log_{2} X = n if 2^{n} = X

For example

log_{2} 32 = 5, because 2^{5} = 32

log_{2} 1024 = 10, because 2^{10} = 1024

Write a program that inputs a number and outputs its base 2 logarithm.
Use floating point input.
This problem would be easy, but the Math package does not have a base 2
logarithm method.
Instead you have to do this:

log_{2} X = (log_{e} X) / (log_{e} 2)

Here, `log`_{e} X

is the natural logarithm of X,
which you can compute using

Math.log( X )

As usual, X is a `double`

.
The user enters floating point numbers:

Enter a double:
998.65
Base 2 log of 998.65 is 9.963835330516641

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## Exercise 4 — Harmonic Mean

The *harmonic mean* of two numbers is given by:

H = 2 / ( 1/X + 1/Y )

This is sometimes more useful than the more usual average
of two numbers.
Write a program that inputs two numbers (as floating point)
and writes out both the usual average (the arithmetic mean)
and the harmonic mean.

Enter X:
12
Enter Y:
16
Arithmetic mean: 14.0
Harmonic mean: 13.714285714285715

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