Which of the following best explains how the density of a submarine is controlled?

• A. By adjusting the amount of water in its ballast tanks
• B. By increasing the speed at which it moves
• C. By changing the temperature of the water around it
• D. By altering the shape of its hull

Answer: (A)

Verified step by step guidance

1. Understand that density is defined as mass divided by volume, expressed as \(\text{density} = \frac{\text{mass}}{\text{volume}}\).
2. Recognize that a submarine controls its overall density to either sink or float by changing its mass without significantly changing its volume.
3. Identify that the submarine adjusts the amount of water in its ballast tanks to change its mass: taking in water increases mass and density, causing it to sink; expelling water decreases mass and density, causing it to rise.
4. Note that increasing speed or changing the temperature of the surrounding water does not directly affect the submarine's density in a controlled way.
5. Understand that altering the shape of the hull affects hydrodynamics but does not significantly change the submarine's density.