WHS AP Physics 2
Fluids Review
1. A sailboat at rest on a calm lake has its anchor dropped a distance of 4.0 m below the surface of the water. The
anchor is suspended by a rope of negligible mass and volume. The mass of the anchor is 50 kg, and its volume is
6.25 x 10-3 m3 . The density of water is 1000 kg/m3.
(a) On the dot below that represents the anchor, draw and label the forces (not components) that act on
the anchor.
(b) Calculate the magnitude of the buoyant force acting on the anchor. If you need to draw anything other
than what you have shown in part (a) to assist in your solution, use the space below. DO NOT add
anything to the figure in part (a).
(c) Calculate the tension in the rope. If you need to draw anything other than what you have shown in part
(a) to assist in your solution, use the space below. DO NOT add anything to the figure in part (a).
(d) The bottom of the boat is at a depth d below the surface of the water. Suppose the anchor is lifted back
into the boat so that the bottom of the boat is at a new depth d’ below the surface of the water. How
does d’ compare to d ?
____ d’ < d ____ d’ = d ____ d’ > d
Justify your answer.
2. A large rectangular raft (density 650 kg/m3) is floating on a lake. The surface area of the top of the raft is 8.2
m2 and its volume is 1.80 m3. The density of the lake water is 1000 kg/m3.
(a) Calculate the height h of the portion of the raft that is above the surrounding water.
(b) Calculate the magnitude of the buoyant force on the raft and state its direction.
(c) If the average mass of a person is 75 kg, calculate the maximum number of people that can be on the raft
without the top of the raft sinking below the surface of the water. (Assume that the people are evenly
distributed on the raft.)
3. A large tank, 25 m in height and open at the top, is completely
filled with saltwater (density 1025 kg/m3). A small drain plug
with a cross-sectional area of 4.0 x 10-5 m2 is located 5.0 m from
the bottom of the tank.
The plug breaks loose from the tank, and water flows from the
drain.
(a) Calculate the force exerted by the water on the plug before
the plug breaks free.
(b) Calculate the speed of the water as it leaves the hole in the side of the tank.
(c) Calculate the volume flow rate of the water from the hole.
4. Three objects of identical mass attached to strings are suspended in a large tank of liquid, as shown above.
(a) Must all three strings have the same tension?
____ Yes ____ No
Justify your answer.
Object A has a volume of 1.0 x 10-5 m3 and a density of 1300 kg m3. The tension in the string to which
object A is attached is 0.0098 N.
(b) Calculate the buoyant force on object A.
(c) Calculate the density of the liquid.
(d) Some of the liquid is now drained from the tank until only half of the volume of object A is submerged.
Would the tension in the string to which object A is attached increase, decrease, or remain the same?
____ Increase ____ Decrease ____ Remain the same
Justify your answer.
5. An underground pipe carries water of density 1000 kg/m3 to a fountain at ground level, as shown above. At
point A, 0.50 m below ground level, the pipe has a cross-sectional area of 1.0 x 10-4 m2. At ground level, the
pipe has a cross-sectional area of 0.50 x 10-4 m2. The water leaves the pipe at point B at a speed of 8.2 m/s.
(a) Calculate the speed of the water in the pipe at point A.
(b) Calculate the absolute water pressure in the pipe at point A.
(c) Calculate the maximum height above the ground that the water reaches upon leaving the pipe vertically at
ground level, assuming air resistance is negligible.
(d) Calculate the horizontal distance from the pipe that is reached by water exiting the pipe at 60° from the level
ground, assuming air resistance is negligible.
6. The radius of the human aorta is about 1.0 cm and the blood passing through it has a speed of about 30 cm/s.
A typical capillary has a radius of about 4 x 10-4 cm, and blood flows through it at a speed of about 5 x 10-4 m/s.
Estimate how many capillaries there are in a body.
7.During a windstorm, a 35.5 m/s wind blows across the flat roof of a small house, as seen below. Find the
difference in pressure between the air inside the home and the air just above the roof, assuming the doors and
windows in the house are closed. The density of air is 1.29 kg.m3.
8. What is the lift (in Newtons) due to Bernoulli’s Principle on a wing of area 80 m 2 if the air passes over the top
and bottom surfaces at speeds of 340 m/s and 290 m/s respectively?