# PhysicsA Density Problem and a Mass Problem

#### geissingert

##### New member
Hoping you can give input. I need you to show work and explain. Here is what we have:

1. A gold coin has a mass of 9.25 grams. What is its volume if the density of gold is 19300 kg/m3?

v= m/d

v= m 9.25 g/d 19300kg/m3

2. A helium filled balloon has a volume of 4.5 m3. What mass of helium does it hold if the density of helium is 1.8x 10-4 g/cm3?

v=4.5 m3
d=1.8x10-4g/cm3
m=dxv

m= 1.8x10-4g/cm3x4.5m3

100cm/1m
m3/m=m2

100cm/1mx100cm/1mx100cm/1m

1000000

m=1.8x10-4 gx4.5 x100x100x100

1.8 x100x100x100

1.000008
180 x 4.5= 810
m=810 (My answer, is this correct?)

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#### Ackbach

##### Indicium Physicus
Staff member
On problem 1, you have the right idea, but you have mixed units: grams versus kilograms. Make sure you have consistent units! So your computation should be
$$V=\frac{m}{\rho}=\frac{9.25\times 10^{-3}\;\text{kg}}{1.93\times 10^{4}\;\text{kg/m}^{3}}=\dots$$
The same exact issue plagues your second problem. You must get consistent units! Either convert your volume to cubic centimeters, or convert your density to kilograms per cubic meter.