Video Transcript
A container that is under the sea,
near the shore, is full of water. The container is suspended above
the seabed on a pole. Water can enter and leave the
container through four holes. Water pressure at one of the holes
in the walls is 7,500 pascal. Which of the following is
correct? (A) The water pressure at all the
holes is 7,500 pascal. (B) The water pressure at holes I
and II is 7,500 pascal, but the pressure at hole III is not equal to 7,500
pascal. (C) The water pressure at hole I is
also 7,500 pascal, but the pressures at holes II and III are not equal to 7,500
pascal.
In this question, we are told that
a box is submerged in the sea above the sea bed. We are given a diagram of the box
and the four holes that water can enter and leave through. Three of the holes are on different
sides of the box, these being holes I, II, and the hole on the right side of the
box. The fourth hole, hole III, is on
the bottom of the box. We were told that the pressure at
one of the holes along the side of the box is 7,500 pascal. Let’s remember some information
about the pressure that fluid exerts on objects and then take a look at the holes in
our box and what we can learn from the diagram.
Recall that Pascal’s principle
states that the pressure exerted by a fluid at a point is the same in all
directions. Also, it will be helpful to
remember that the pressure exerted by a fluid at two points that are at the same
height are equal, as long as the only pressure being exerted is due to the weight of
the fluid. Now, let’s look at the diagram and
see what we can learn from it. We can see that the hole on the
right-hand side is at a pressure of 7,500 pascal. If we look at the uppermost
diagram, which shows hole I, we can see that it is at the same height as the hole
with the labeled pressure. And we know that the pressure
exerted at two points that are at the same depth are equal. This means that the pressure at
hole I must be equal to 7,500 pascal as well.
Moving on to the middlemost
diagram, which depicts hole II, we can see that this is also at the same height as
the hole labeled 7,500 pascal and hole number I. Therefore, this hole will also be
at the same pressure of 7,500 pascal.
Now, looking at the lowest diagram,
which shows hole III, we can see that, unlike the other three holes, it is not at
the same depth. It is on the floor of the box,
lower than the other holes. This means it will have a different
pressure than the other holes. Because the bottom of the box is at
the greatest depth, it will have the greatest pressure of all of the holes. So holes number I and II will be at
the same pressure of 7,500 pascal, while hole number III will be at a pressure not
equal to that. Therefore, option (B) is the
correct answer.
