Anything less dense than water will float, like oil. Anything more dense than water will sink, like rock.
Answer:
Part a)

Part b)

Explanation:
As per momentum conservation we know that there is no external force on this system so initial and final momentum must be same
So we will have




Part b)
By equation of kinetic energy we have




We want to find the combined volume of 3 tennis balls. We will get that the combined volume is 493.7 cm^3
First, remember that for a sphere of diameter D, the volume is:

Where 3.14 is pi.
Here we know that the average diameter of a tennis ball is 6.8cm, then we can replace that in the above equation to find the volume (in average) of a single tennis ball:

Now, in 3 balls of tennis, the combined volume will be 3 times the above one, this is:

If you want to learn more about volumes, you can read:
brainly.com/question/10171109
Explanation:
Crust...molten
a. Oceanic, iron
b. Continental, silicates
c. less
3. Mantle, Denser
a. Lithosphere
b. Asthenosphere
4. Core
a. elements, rocks
b. liquid, magnetic
(I guess the liquid should come after the is)
Couldn't answer all but wanted to help