Good afternoon!
We calculate the volume of the container in cm³. To do that, we must put the units in cm:
30 cm → 30 cm
50 mm → 5 cm
0.2 m → 20 cm
The volume is:
V = 30 . 5 . 20
V = 3000 cm³
Now, we calculate the mas with the formula:
m = dV
m = 2.5 · 3000
m = 7500 g
Dividing by 1000, we have the mass in kg:
m = 7.5 kg
A. Angular momentum is always conserved would be the correct answer.
This is because like linear momentum (mvmv), angular momentum (r×mvr×mv) is a conserved quantity, where rr is the vector from the center of rotation. For a skater holding a static pose, for each particle making up her body, the contribution in magnitude to the total angular momentum is given by mirivimirivi. Thus bringing in her arms reduces riri for those particles. In order to conserve angular momentum, there is then an increase in the angular velocity.
hope this helps!