1. a wall is made up of four elements, as follows: ½” wood siding r = 0.81 ½” plywood sheathing r = 0.62 3½” fiberglass insulation r = 10.9 ½” sheetrock r = 0.45 (units of r-value are ft2-hr-of/btu) a. what is the total r-value of the wall? b. what is the r-value if no insulation is installed? c. in which direction (in or out) would the heat flow when the outside temperature is 90of and the temperature inside is 70of?

Part A)

Since all four resistors are made up of different elements and connected in series

SO in series the net resistance is given by

Part B)

If insulation is removed then resistance due to three materials

Part c)

Heat will always flow from High temperature to low temperature

So here heat flow is from 90 degree F to 70 degree F

so it will flow from outside to inside

causes

fossil fuels burn

cities become more industrialized

human population grows worldwide

3. dark matter

empty space could also be a simple vacuum