Question

The density of balsa wood is 7.8 pounds per cubic foot. What is the weight, in kilograms, of a piece of balsa wood 4.0 inches by 6.0 inches by 20.0 inches.

Answer 1

density = mass/volume

do you know the volume of the piece in square inches?

Answer 2

is it 480

Answer 3

the volume

Answer 4

correct

Answer 5

do you know what units it is in?

Answer 6

the volume?

Answer 7

480 c^3

Answer 8

in^3

Answer 9

inches cubed

Answer 10

no idea what the c is for

Answer 11

all units work like this btw

Answer 12

ok so all you have to do is convert cubic inches to cubic feet

Answer 13

because we know density of the wood is

7.8lbs/ft^3

Answer 14

we always want to work with like units hen trying to figure stuff like this out

Answer 15

can you convert it over or do you need me to explain how?

Answer 16

expplain please

Answer 17

I'm going to show you exactly the same thing I showed you last time hopefully it makes sense to you this time :D

12 inch = 1 feet

Convert them to squared units
12 inch*12inch = 1 feet*1feet
=
144inch^2 = 1 feet^2

Now convert them to cubic units
144inch^2*12inch = 1 feet^2*1 feet
=
1728inch^3 = 1 feet^3

If we wanted to convert them to the power 4 we would keep doing this,
1728inch^3 * 12inch = 1 feet^3*1 feet
=
20736inch^4 = 1 feet^4

So in summery to get to cubic units from just regular feet and inches
12 inch*12inch*12inch = 1 feet*1 feet*1 feet
=
1728inch^3 = 1 feet^3



Next to convert over we simply make a ratio up we want to eliminate inches and be left with feet so we put feet in the numerator and put inches in the denominator.

Think of the units kind of like numbers when you divide something by itself you always get 1 which when multiplied by anything just gives back anything unchanged.

For example

1/1 = 1
3333/3333 = 1

43434/43434 = 1

etc.

\[\frac{{1feet^3}}{1738inch^3}*480inch^3\]
\[\frac{1feet^3*480inch^3}{1738inch^3}\]

Answer 18

get it?

Answer 19

yesh thanks

Answer 20

so anwer would be .276

Answer 21

right