EK Fluids

[deleted388502]

514. The ocean is able to permanently support a battleship because:

A. the ocean is heavier than the battleship
B. the metal of the battleship is less dense than ocean water
C. at the point of contact, the forces exerted by the battleship are perpendicular to the surface of the water
D. the volume of water displaced by the battleship is equal to the volume of the battleship resting below the surface

Answer is C, confused as to why it wouldn't be D because could this not be explained by buoyancy?
Thanks!

---

Members don't see this ad.

 

[justadream]

@avenlea

I'm sure someone has a better answer but if you define "support a battleship" as "being above the water", then imagine a scenario where the average density of the battleship = density of seawater.

In this case, D would hold true but the ship would be like in between the surface and the bottom of the ocean.

 

[Chrisz]

@avenlea, D is not an explanation, it is simply a phenomenon observed when a boat is floating. We have choose the answer which explain why the boat is floating, not an answer that simply describes the phenomenon. The boat floats because we have to provide a force that is necessary to counter the gravity. You know the gravitational force acts pulling downward on the boat,, and the gravitational force is perpendicular to the surface of water. the water has to provide a net force, called float force, that is equal to gravitational force in magnitude but in the opposite direction of gravitational force to counter the gravitational force. According to newton's reaction law, when one object exerts a force on a second object, the second object also exerts a force with equal magnitude but opposite in direction on the first object. Since water exerts a force on the boat with upward direction, perpendicular to the surface, the boat also exerts a force with equal magitude but opposite in direction on water. This means the force exerted by boat on water is also perpendicular to the surface of water.

 

[Chrisz]

I think a graph would be easier for you to understand. Below is a graph I drew. I am not good at drawing, hope you would not mind

 

[deleted388502]

Thank you all! @Chrisz, your explanation was golden. Appreciate the time you took to draw out a picture!