An ornamental spherical ball made of bronze has an outer diameter of 1.2m cm and a uniform thickness of 13cm. If bronze weighs 8.5 grams / cm^3, find the weight of the ball.
1. Calculate the volume of the bronze which is the difference between the outer sphere and the inner sphere.
Convert all measures into cm. If $\displaystyle r_o$ denote the outer radius and $\displaystyle r_i$ the radius of the inner sphere then the volume of the bronze is:
$\displaystyle V_{bronze}=\frac43 \cdot \pi \left(r_o^3-r_i^3 \right)$
2. Since $\displaystyle density = \frac{mass}{volume}~\implies~mass=density \cdot volume$
3. Use the result from 1. to calculate the mass of the bronze.
4. If you are actually asked to find the weight of the bronze you have to multiply the result from 3. by $\displaystyle 0.00981\ \frac Ng$
Spoiler: