Khan Academy Chapter 4: Fluids

A hydraulic system is designed to allow water levels to change depending on a force applied at the top of a tank. If a force, F1, of 4N is applied to a square, flexible cover where A1=16, and the area of A2=64, what force must be applied to A2 to keep the water level from changing?

16 N F1/A1=F2/A2

A tank with height y is filled with water to the top and is placed at a height z above the ground. Currently the water level is 3.0 meters above the ground. At the bottom of the tank, there is a hole where the water can flow out when needed. Which of the following would increase the flow rate? A. Increase the size of the hole B. Increase z C. Decrease the size of the hole to increase the velocity out of the hole D. Increase y and z without adding additional water

A. Increase the size of the hole

When the gauge pressure is doubled, what happens to the absolute pressure? A. It increases by a factor less than 2. B. It stays the same. C. It doubles. D. It is halved.

A. It increases by a factor less than 2.

A water tower operator is interesting in increasing the pressure of a column of water that is applied to a piston. How should the speed of the water be changed to increase the pressure and the force? A. Increase the speed B. Decrease the speed C. Release water intermittently against the pipe D. The speed of the water will not change the pressure at the piston.

B. Decrease the speed At equal heights, speed and pressure of a fluid are inversely related.

According to your understanding of Bernoulli's principle and continuity equation, which of the following statements accurately describes the phenomenon of vascular flutter which occurs when an artery becomes constricted due to the accumulated plaque in its inner walls? A. Constriction in the blood vessel causes backup and the pressure to build before the narrowing. B. The constriction causes the pressure to drop and the vessel to collapse. C. The constriction will cause the blood to travel faster and the extra blood will create pressure after the narrowing. D. Constriction in the blood vessel causes the pressure to build up right at the narrowing.

B. The constriction causes the pressure to drop and the vessel to collapse.

A hydraulic lever is used to lift a heavy hospital bed, requiring an amount of work, W. When the same bed with a patient is lifted, the work required is doubled. How can the cross sectional area of the platform on which the bed is lifted be changed so that the pressure on the hydraulic lift remains constant? A. The cross sectional area must be halved. B. The cross sectional area must be doubled C. The cross sectional area must be divided by four D. The cross sectional area must remain constant.

B. The cross sectional area must be doubled

Which of the following scenarios most accurately represents Pascal's law? A. A person pushes the brake with a small area with a small force over a short distance to produce an equivalent force to stop the car. B. The volume displaced by piston 1 is equal to the volume displaced by piston 2 in a hydraulic lift. C. When a pregnant mother is riding in a car that crashes, the fluid surrounding the fetus will help to dissipate any force from the crash. D. When you push down on the stopper of a big water jug with 10 N, the same force of 10 N is transmitted undiminished to the larger bottom surface of the jug.

B. The volume displaced by piston 1 is equal to the volume displaced by piston 2 in a hydraulic lift.

Which of the following is NOT characteristic of a liquid with laminar flow? A. little lateral mixing B. presence of eddies C. low velocity D. high viscous forces

B. presence of eddies

A gold crown recently acquired is suspected to be brass covered in gold. The crown weighs 25.0 N in air and has an apparent weight of 22.5 N in fresh water. Based on these results, which of the following conclusions is correct? (density of gold = 19,300 kg/m^3, density of brass= 8300-8700 kg/m^3 A. It is likely that the crown is made of half brass and half gold. B. It is likely that the crown is made of brass only. C. It is likely that the crown is made of brass covered in gold. D. It is likely that the crown is made of gold only.

C. It is likely that the crown is made of brass covered in gold. 25.0-22.5= 2.5N 2.5N= 1000 kg/m^3 x V x 10 m/s^2 = 2.5 x 10^-4 mass of the crown=25.0/10 = 2.5kg density of the crown = 2.5/2.5 x 10^-4 =10,000 kg/m^3

The speed of blood in the aorta is much higher than the speed of blood through a capillary bed. How can this be explained using the continuity equation, assuming that we are interested in average flow, and there is no net fluid loss? A, The aorta is located higher than the capillary bed B. The pressure in the aorta is the same as the pressure in the capillary bed. C. The cross sectional area of all the capillaries added together is much greater than the cross sectional area of the aorta D. The cross sectional area of a capillary is much smaller than the cross sectional area of the aorta

C. The cross sectional area of all the capillaries added together is much greater than the cross sectional area of the aorta

Which of the following data sets is sufficient to determine the linear speed through an area of a rigid pipe? A. The cross sectional area in another segment of the pipe and the cross sectional area in the region of interest B. The reynolds number, viscosity of the fluid, density, and diameter of the pipe C. The radius of the pipe, pressure gradient, viscosity and length of the pipe D. The absolute pressure and density

C. The radius of the pipe, pressure gradient, viscosity and length of the pipe

There is a 1-liter container filled with 500 milliliters of water placed on top of a scale displaying 80 pounds. When a metal cube is submerged tied to a string end into the container, which of the following statements accurately describes the result? A. The scale will remain at 80 pounds unless the cube touches the bottom of the bowl. B. The scale will remain at 80 pounds until the cube is floating on top of the water fully submerged. C. The cube's density must be provided to predict what will happen. D. The scale will register a weight greater than 80 pounds due to Newton's Third Law.

D. The scale will register a weight greater than 80 pounds due to Newton's Third Law.

On which of the following does the buoyant force on an object floating on the surface of a liquid most directly depend? A. mass of the liquid B. volume of the object C. viscosity of the liquid D. density of the liquid

D. density of the liquid F=p(fluid)v(displaced)g