### Home > PC3 > Chapter 4 > Lesson 4.1.3 > Problem4-46

4-46.

​Heat loss, $h$, per hour through a glass window varies directly with the difference between the indoor and outdoor temperature, $d$, and inversely with the thickness of the glass, $g$.

1. Write an equation that will calculate the heat loss based on the difference of the temperature and the thickness of the glass. Do not forget the constant of proportionality!

$h=\frac{kd}{g}$

2. The Johnson family has a window that is $0.3$ cm thick that loses $2.4$ BTU of energy each hour when the outside temperature is $50º\text{F}$ and the inside temperature is $70º\text{F}$. Use this information to determine the constant of proportionality.

$2.4=\frac{k(70-50)}{0.3}$

3. The Johnson’s decide to replace the window with one that is $1.5$ cm thick. How much energy will be lost if the inside temperature is $70º\text{F}$ and the outside temperature is $30º\text{F}$?

Use your formula from part (a).