Question 1

The reason fast-moving water makes noise is
A) vortices.
B) chaos.
C) laminar flow.
D) turbulence.

Accepted Answer

Turbulence in fast-moving water creates irregular fluctuations and mixing, which generates noise.

Question 2

The pressure in a water pipe is always lower in regions where the water moves faster only when
A) the pipe increases in altitude towards the faster fluid end
B) the pipe is level.
C) anything other than water is in the pipe
D) the pipe is made of plastic

Accepted Answer

According to Bernoulli's principle, in a horizontal pipe, the pressure is lower where the fluid velocity is higher. This is because the sum of pressure energy, kinetic energy, and potential energy per unit volume is constant along a streamline.

Question 3

Flowing honey is less likely to become turbulent than flowing water because
A) honey's large density favors laminar flow.
B) water's large viscosity favors turbulent flow.
C) water's large pressure favors turbulent flow.
D) honey's large viscosity favors laminar flow.

Accepted Answer

Honey's large viscosity reduces its tendency to form eddies and chaotic flow patterns, favoring laminar flow, where the fluid flows in parallel layers with minimal disruption between them.

Question 4

To set the world land speed record and travel faster than the speed of sound, the Thrust SSC vehicle used two jet engines that produced about a 250,000 horsepower. The principal reason why this car needed so much power to travel so fast is that
A) a car's momentum is proportional to its power, so reaching very high momentum requires very high power.
B) the pressure drag on a car increases dramatically as the car's speed increases.
C) the force of the car's momentum was enormous and the jet engines were needed to supply that force.
D) Newton's second law requires a very fast moving object to have a very large acceleration and thus a very large force.

Accepted Answer

The primary reason Thrust SSC required such immense power is due to the dramatic increase in pressure drag as the vehicle's speed increases, especially as it approaches and surpasses the speed of sound. This drag force rises significantly with speed, necessitating more power to overcome it and achieve record-breaking velocities.

Question 5

As air flows through the horizontal ductwork in a warehouse, it passes through a fan inside the duct and the air's total energy increases. Since the air's speed doesn't change as the result of going through the fan, you know that the air's
A) kinetic energy has decreased but its pressure has remained the same.
B) kinetic energy has increased but its pressure has remained the same.
C) pressure has decreased but its kinetic energy has remained the same.
D) pressure has increased but its kinetic energy has remained the same.

Accepted Answer

Since the air's speed doesn't change, its kinetic energy remains the same. The increase in total energy must therefore come from an increase in pressure.

Question 6

You are taking a shower in your dormitory when someone flushes a toilet nearby. The pressure in the cold water line drops and you find yourself showering in what feels like molten lava. This loss of cold water pressure occurs when the toilet lets cold water flow through the pipes delivering it to the bathroom and the water's speed in those pipes increases. Assuming all the piping to be about on the same level, the cold water's faster motion in the delivery pipes reduces its pressure in the shower head because faster moving water
A) has less pressure than slower moving water.
B) has less kinetic energy than slower moving water.
C) has less gravitational potential energy than slower moving water.
D) losses more energy to viscous drag as it flows through the delivery pipes.

Accepted Answer

A) The principle that explains this phenomenon is Bernoulli's principle, which states that an increase in the speed of a fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy. Therefore, when the cold water flows faster to fill the toilet, its pressure in the shower head decreases, making the hot water feel relatively hotter.

Question 7

A stream of smoothly flowing water arcs through the air and hits the side window of a house. At the surface of the window, right where the stream of water hits it, the water's pressure is
A) lower than atmospheric and the water's speed is faster than in the stream.
B) higher than atmospheric and the water's speed is faster than in the stream.
C) higher than atmospheric and the water's speed is slower than in the stream.
D) lower than atmospheric and the water's speed is slower than in the stream.

Accepted Answer

According to Bernoulli's principle, when a fluid in steady flow hits a surface and spreads out, its speed decreases, and its pressure increases relative to the conditions in the stream. Therefore, at the point where the water hits the window and spreads out, its speed is slower, and its pressure is higher than atmospheric pressure.

Question 8

The top surface of a calm, smoothly flowing stream is always at atmospheric pressure. As water in this stream runs into a tree stump and slows almost to a stop, the water's top surface
A) shifts upward slightly above the normal stream level.
B) shifts downward slightly below the normal stream level.
C) stays at the same height and does not begin to rotate.
D) stays at the same height but begins to rotate clockwise as viewed from above.

Accepted Answer

When water slows down, such as when it encounters an obstacle like a tree stump, the kinetic energy of the water is converted into potential energy, causing the water level to rise slightly. This is in accordance with the principle of conservation of energy.

Question 9

You construct a water-powered go-cart by attaching a large tank of water to a cart. The water can be forced out a nozzle by connecting a tank of high-pressure air to the water tank. In preparation for your first ride, you position this contraption facing away from a brick wall. You climb on and start spraying the water against the wall. To your delight you accelerate away from the wall and begin to move. When you have moved far enough away from the wall that the stream of water can no longer hit it, you
A) continue to accelerate as the water sprays out the back of the cart.
B) continue to move, but stop accelerating since the water can no longer push against the wall.
C) feel lighter than normal since the water hitting the ground will produce an upward force.
D) continue to accelerate, but less since it takes more force to accelerate a moving object than a stationary one.

Accepted Answer

The cart continues to accelerate due to the principle of conservation of momentum. As water is expelled in one direction, the cart is propelled in the opposite direction, regardless of whether the water hits a wall or not.

Question 10

You are caulking a window. The caulk is rather thick and, to lay the bead correctly, the exit nozzle is small. A caulking gun uses a plunger which is operated by pulling back on a handle. You must squeeze the handle very hard to get the caulk to come out of the narrow opening because
A) pressure is distributed uniformly throughout the fluid and the area of the plunger is much larger than the area of the opening.
B) viscous drag between the walls of the tip and the caulk causes the caulk to swirl around chaotically.
C) Newton's third law requires most of the energy in the caulk to be used to push back on the plunger rather than moving it through the tip.
D) the high density of the caulk impedes its flow through the small opening.

Accepted Answer

The principle that pressure is distributed uniformly throughout a fluid and the fact that the area of the plunger is much larger than the area of the opening means that a high force must be applied to the plunger to achieve the necessary pressure to push the caulk through the narrow opening. This is a direct application of Pascal's law.

Question 11

When you pour honey into a bowl, it flows smoothly. If you did the same with water, it would splash. These different behaviors occur because honey's high
A) viscosity keeps it flowing smoothly while water's low viscosity allows inertia to break its flow into many separate pieces.
B) momentum keeps it moving in a straight line while water's low momentum allows it to turn abruptly in many different directions.
C) density keeps it flowing smoothly while water's low density allows it to float upward and splash about.
D) mass keeps it flowing smoothly while water's low mass allows it to acquire lots of angular momentum.

Accepted Answer

Honey's high viscosity means it flows more slowly and smoothly, resisting sudden movements, while water's low viscosity means it can easily be disrupted and splash.

Question 12

A squirt gun is a simple type of water pump in which a plunger attached to the trigger forces water out of a nozzle and across the room. When you squeeze the trigger of the gun, water squirts out of the nozzle because
A) the pressure inside the gun is higher than atmospheric pressure.
B) the water is compressed at the plunger so it must expand out the nozzle.
C) the Bernoulli effect causes the pressure of water leaving the nozzle to be less than atmospheric pressure.
D) the Bernoulli effect causes the water's overall energy to increase as it travels through the narrow nozzle.

Accepted Answer

When you squeeze the trigger of a squirt gun, the plunger forces water out, increasing the pressure inside the gun above atmospheric pressure, causing water to squirt out.

Question 13

Reliving the "good old days" several physics faculty decide to spend a warm balmy summer's day squirting each other with garden hoses right in front of the physics building. They place their thumb over the end of the hose, and the water squirts out very quickly, because their thumb increases
A) the energy of the water.
B) the potential energy in the hose.
C) the pressure of the water in the hose
D) the speed of the water in the hose.

Accepted Answer

Placing a thumb over the end of the hose decreases the area through which water can exit, increasing the pressure inside the hose, which in turn increases the speed of the water exiting the hose.

Question 14

You are filling a jar of honey from the spigot at the bottom of a large barrel at the grocery store. The honey flows extremely slowly, so the store manager has the barrel refilled. Now the honey flows much more rapidly from the spigot because
A) the pressure of the honey at the bottom of the barrel increases as the height of honey in the barrel increases.
B) the density of the honey decreases as the height of the honey in the barrel increases.
C) the viscosity of the honey decreases as the height of honey in the barrel increases.
D) the viscosity of the honey increases as the height of honey in the barrel increases.

Accepted Answer

The pressure at the bottom of the barrel increases with the height of the honey, which increases the force pushing the honey out of the spigot, making it flow more rapidly.

Question 15

As the Reynolds number increases,
A) flow is becoming more laminar.
B) flow is going from being viscous dominated to inertia dominated and therefore turbulent.
C) flow is slowing down.
D) flow is speeding up.

Accepted Answer

The Reynolds number is a dimensionless quantity used in fluid mechanics to predict flow patterns in different fluid flow situations. As the Reynolds number increases, it indicates a transition from laminar (smooth) flow to turbulent flow, meaning the flow is moving from being dominated by viscous forces to being dominated by inertial forces.

Question 16

You have just set up a weather station for your daughter to observe wind speeds at home. You had to move it up from the ground because when it was too close to the ground the wind speed readings are all too small. This is because
A) The air near the ground is too dense to move well.
B) The ground is hot so air movement there is always upward, never sideways.
C) The boundary layer of a moving fluid moves slower than at other points farther into the fluid.
D) Someone kept stepping on the wind speed gauge.

Accepted Answer

The boundary layer concept explains that the layer of fluid (in this case, air) directly in contact with the surface (ground) moves slower than the layers above it due to friction between the fluid and the surface. This results in lower wind speed readings close to the ground.

Question 17

Briefly discuss four properties of a fluid that determine whether it exhibits turbulent or laminar flow.

Accepted Answer

The answer of Briefly discuss four properties of a fluid...

Question 18

The onset of turbulent flow happens for a Reynolds number of about
A) 2300
B) 5000
C) 0
D) Infinity

Accepted Answer

The onset of turbulent flow typically occurs at a Reynolds number of about 2300. Below this value, flow tends to be laminar, and above it, flow starts to transition to turbulent.

Question 19

The diameter of a pipe is tripled while the pressure difference across the pipe remains the same. The volume flow rate of the pipe increases by a factor of
A) 3
B) 9
C) 27
D) 81

Accepted Answer

The answer of The diameter of a pipe is tripled...

Question 20

Suppose you work in the E.R. and a choking patient comes in with their trachea half obstructed. (The diameter is half of what it was before the obstruction.) You manage to correct the problem and send them on their way safely, explaining that such obstructions are particularly dangerous because
A) a half - blocked airway passes only 1/4 the regular amount of air.
B) a half - blocked airway passes only 1/16 the regular amount of air.
C) a half - blocked airway passes only 1/2 the regular amount of air.
D) a half - blocked airway passes only 1/32 the regular amount of air.

Accepted Answer

The flow of air through the trachea is proportional to the fourth power of the radius (Poiseuille's Law). If the diameter is halved, the radius is also halved, and the flow is reduced to (1/2)^4 = 1/16 of the original flow.

Quiz 6: Fluids and Motion

The reason fast-moving water makes noise is

The pressure in a water pipe is always lower in regions where the water moves faster only when

Flowing honey is less likely to become turbulent than flowing water because

To set the world land speed record and travel faster than the speed of sound, the Thrust SSC vehicle used two jet engines that produced about a 250,000 horsepower. The principal reason why this car needed so much power to travel so fast is that

As air flows through the horizontal ductwork in a warehouse, it passes through a fan inside the duct and the air's total energy increases. Since the air's speed doesn't change as the result of going through the fan, you know that the air's

A stream of smoothly flowing water arcs through the air and hits the side window of a house. At the surface of the window, right where the stream of water hits it, the water's pressure is

The top surface of a calm, smoothly flowing stream is always at atmospheric pressure. As water in this stream runs into a tree stump and slows almost to a stop, the water's top surface

You are caulking a window. The caulk is rather thick and, to lay the bead correctly, the exit nozzle is small. A caulking gun uses a plunger which is operated by pulling back on a handle. You must squeeze the handle very hard to get the caulk to come out of the narrow opening because

When you pour honey into a bowl, it flows smoothly. If you did the same with water, it would splash. These different behaviors occur because honey's high

A squirt gun is a simple type of water pump in which a plunger attached to the trigger forces water out of a nozzle and across the room. When you squeeze the trigger of the gun, water squirts out of the nozzle because

Reliving the "good old days" several physics faculty decide to spend a warm balmy summer's day squirting each other with garden hoses right in front of the physics building. They place their thumb over the end of the hose, and the water squirts out very quickly, because their thumb increases

You are filling a jar of honey from the spigot at the bottom of a large barrel at the grocery store. The honey flows extremely slowly, so the store manager has the barrel refilled. Now the honey flows much more rapidly from the spigot because

As the Reynolds number increases,

You have just set up a weather station for your daughter to observe wind speeds at home. You had to move it up from the ground because when it was too close to the ground the wind speed readings are all too small. This is because

Briefly discuss four properties of a fluid that determine whether it exhibits turbulent or laminar flow.

The onset of turbulent flow happens for a Reynolds number of about

The diameter of a pipe is tripled while the pressure difference across the pipe remains the same. The volume flow rate of the pipe increases by a factor of

Suppose you work in the E.R. and a choking patient comes in with their trachea half obstructed. (The diameter is half of what it was before the obstruction.) You manage to correct the problem and send them on their way safely, explaining that such obstructions are particularly dangerous because