Well, they are already giving us the density of gold (Au) which makes our life easier.
The easiest way to remember is DMV as in Department of Motor Vehicles.
They are also giving us the dimensions of the Gold Bar. Remember, we are not given the volume but we are given the 3 dimensions to figure out the volume. Volume can be figured by multiplying length, width and height:
V= (L)(W)(H)
Since its a bar length is longer than both width and height. Therefore, l=0.200m, w=.100m, h=.100m. But, the volume in the density of Gold is expressed in cm3 so once we multiply our dimensions we will get m3 and we wont be able to cancel em out. Therefore, we must change all the dimensions from m to cm.
1 m = 100 cm, therefore: l=(.200)(100)= 20 cm
w=(.100)(100)= 10 cm, same height as well.
so volume =
Now that we know the density and volume, mass can be easily calculated by:
(remember dmv)
Therefore:
cm
3 cancel out because :
so we get:
most of the time m is answered in Kg so,
Hopefully that helped = ) If you have any questions please let me know.