Test 3 Physics

1.

1 point

In 1971, astronaut Alan Shepard hit a golf ball on the moon. How did the absence of air affect the ball’s flight?

There was no significant difference, as a golf ball is designed to have no drag.

The absence of air makes the ball go farther.

There was zero drag on the ball, only the moon's gravity.

Not certain, as it would depend whether the golf ball had dimples or not.

2.

1 point

Why must tall dams be so much thicker at their bases than at their tops?

The pressure is greater at the bottom due to greater pressure at the top.

The greater the depth of the water the greater the pressure pushing on the wall of the dam.

A tall dam needs a lot of structural support.

The pressure is greater at the bottom due to greater kinetic energy per volume at the top.

3.

1 point

If you ride your bicycle directly behind a large truck, you will find that you don’t have to pedal very hard to keep moving forward. Why?

The air flow around the truck has a large Reynolds number.

The laminar wake behind the truck shields objects in that wake from the air flow around the truck.

The air flow around the truck has a small Reynolds number.

The turbulent wake behind the truck shields objects in that wake from the air flow around the truck.

4.

1 point

When you stand in a pool with water up to your neck, you find that it’s somewhat more difficult to breathe than when you’re out of the water. Why?

The pressure due to the depth of the water above your chest presses in on you.

It is harder to pull air down to that depth.

The air pressure is greater at that depth.

The air in your lungs is at greater pressure.

5.

1 point

A log is much heavier than a stick, yet both of them float in water. Why doesn’t the log’s greater weight cause it to sink?

Wood always floats.

The upward buoyant force on the log is greater than the upward buoyant force on the stick.

The water weighs more than the log.

The upward buoyant force on the log is greater than its weight.

6.

1 point

You seal a rigid container that is half full of hot food and put it in the refrigerator. Why is the container’s lid bowed inward when you look at it later?

The air gets more dense as it gets colder.

The weight of the lid makes it bow inward.

The hot food shrinks as it cools.

The air pressure of the air outside the container pushes the lid in.

7.

1 point

A favorite college prank involves simultaneously flushing several toilets while someone is in the shower. The cold water pressure to the shower drops and the shower becomes very hot. Why does the cold water pressure suddenly drop?

Flushing makes the water in the pipes flow faster, dropping the pressure.

Actually, the flushing increases the hot water pressure rather than lowering the cold water pressure.

Flushing increases the water pressure at the toilets, lowering the pressure at the shower.

The cold water is diverted from the shower to the toilets.

8.

1 point

Each time you breathe in, air accelerates toward your nose and lungs. How does the pressure in your lungs compare with that in the surrounding air as you breathe in?

The pressure in your lungs is equal to that of the surrounding air.

The pressure in your lungs is greater than that of the surrounding air.

There is no specific relationship between the pressure in your lungs and the pressure of the surrounding air.

The pressure in your lungs is less than that of the surrounding air.

9.

1 point

How would a Frisbee fly on the airless moon?

It would fly just like a rock thrown with the same initial velocity.

It would go farther because gravity is weaker.

It would fly farther because of less drag.

The lift forces would be smaller, so it would not fly as far.

10.

1 point

You use your breath to inflate a large rubber tube and then ride down a snowy hill on it. After a few minutes in the snow the tube is underinflated. What happened to the air?

It got cold.

Its pressure decreased.

The moisture in the air (from your breath) froze out.

It leaked out of the tube.

11.

1 point

If you start two identical paper boats from the same point, you can make them follow the same path down a quiet stream. Why can’t you do the same on a brook that contains eddies and vortices?

The brook with eddies and vortices has laminar flow.

Turbulent water flows in unpredictacle directions.

Actually you can, you just have to be very careful.

12.

1 point

Ice tea is often dispensed from a large jug with a faucet near the bottom. Why does the speed of tea flowing out of the faucet decrease as the jug empties?

The gravitational potential energy due to the depth of the tea decreases as the height of the tea decreases.

Pressure decreases as the height of the tea decreases.

There is less tea, so it comes out slower.

As the container empties the air inside expands to fill the volume of the container, creating a suction effect which slows the tea coming out.

13.

1 point

If you seal a soft plastic bottle or juice container while hiking high in the mountains and then return to the valley, the container will be dented inward. What causes this compression?

The air inside the container is at a lower pressure than the air outside.

The air inside the container takes up less volume once the container dents inward.

The mountain air inside is colder and so it is less dense.

The air inside the container is less dense.

14.

1 point

When you swing a stick slowly through the air, it’s silent, but when you swing it quickly, you hear a “whoosh” sound. What behavior of the air is creating that noise?

There is laminar flow around the rapidly-moving stick.

There is a boundary layer of air near the surface of the stick.

The Reynolds number of the air flow is low when the stick moves rapidly.

There is turbulence behind the rapidly-moving stick.

15.

1 point

When a fish is floating motionless below the surface of a lake, what is the amount and direction of the force the water is exerting on it?

Upward, greater than the weight of the fish.

Downward, less than the weight of the fish.

Upward, equal to the weight of the fish.

The water does not exert any force on the fish.

16.

1 point

A baker is decorating a cake by squeezing frosting out of a sealed paper cone with the tip cut off. If the baker makes the hole at the tip of the cone too small, it’s extremely difficult to get any frosting to flow out of it. Why?

The rate at which the frosting flows is inversely proportional to the diameter of the hole.

The rate at which the frosting flows is proportional to the diameter of the hole to the fourth power.

The rate at which the frosting flows is proportional to the diameter of the hole.

The rate at which the frosting flows is proportional to the diameter of the hole to the third power

17.

1 point

Many grocery stores display frozen foods in bins that are open at the top. Why doesn’t the warm room air enter the bins and melt the food?

Fans keep the warm air away.

Warm air does enter the bins, but it's not warm enough to melt the food.

The warm air is blocked from the food by the cold air above the food.

The warm air does enter the bins, but the refrigeration unit keeps the air cold enough to keep the food cold.

18.

1 point

When you mix milk or sugar into your coffee, you should move the spoon quickly enough to produce turbulent flow around the spoon. Why does this turbulence aid mixing?

The turbulence results from a large Reynolds number.

Mixing is more efficient in a turbulent flow than a laminar flow.

The turbulence results from a small Reynolds number.

The turbulence causes the coffee to move quickly in random directions, aiding mixing.

19.

1 point

To drive along a level road at constant velocity, your car’s engine must be running and friction from the ground must be pushing your car forward. Since the net force on an object at constant velocity is zero, why do you need this forward force from the ground?

To counteract the drag force from moving through the air.

To counteract friction with the road.

The forward force must exceed the drag force.

A force is always needed to keep an object moving.

20.

1 point

Pedestrians on the surface of a windswept bridge don’t feel the full intensity of the wind because the air is moving relatively slowly near the bridge’s surface. Explain this effect in terms of a boundary layer.

The air's Reynold's number is decreased by the boundary layer of air near the bridge.

The air just above the bridge is kept from moving by viscous forces, forming a boundary layer.

The air just above the ground is kept from moving by friction, forming a boundary layer.

The air's Reynold's number is increased by the boundary layer of air near the bridge.

21.

1 point

Why must the pressure inside a whistle teakettle exceed atmospheric pressure before the whistle can begin to make noise?

The whistle is due to pressurized (greater than atmospheric pressure) steam forcing its way out through the narrow opening.

When the kettle whistles that means the water inside is boiling.

Boiling makes the steam pressure exceed atmospheric pressure.

22.

1 point

A hurricane or gale force wind can lift the roof off a house, even when the roof has no exposed eaves. How can wind blowing across a roof produce an upward force on it?

A flat roof is perfectly streamlined and this causes a lift force.

Drag forces on the roof drag the roof upward off the house.

The rapidly-moving air above the roof is at a lower pressure than the still air inside the house.

The wind catches the edge of the roof and blows it off.

23.

1 point

Explain why a parachute slows your descent when you leap out of an airplane.

The air flow around the parachute is turbulent with a small turbulent wake, leading to huge pressure drag forces and a relatively small terminal velocity.

The air flow around the parachute is turbulent with a small turbulent wake, leading to huge viscous drag forces and a relatively small terminal velocity.

The air flow around the parachute is turbulent with a large turbulent wake, leading to huge pressure drag forces and a relatively small terminal velocity.

The air flow around the parachute is turbulent with a large turbulent wake, leading to huge viscous drag forces and a relatively small terminal velocity.

24.

1 point

Many jars have dimples in their lids that pop up when you open the jar. What holds the dimple down while the jar is sealed, and why does it pop up when the jar is opened?

The air inside is less dense than the air outside. When the lid is opened, the densities equalize, and the dimple pops back to its normal position.

The air inside is more dense than the air outside. When the lid is opened, the densities equalize, and the dimple pops back to its normal position.

The air outside is at higher pressure than the air inside the jar, which holds the dimple down. When the pressure equalizes, the dimple pops back to its normal position.

The air inside the jar is at higher pressure than the air outside, which holds the dimple down. When the pressure equalizes, the dimple pops back to its normal position.

25.

1 point

A helium-filled balloon floats in air. What will happen to an air-filled balloon in helium? Why?

It will sink because helium is denser than air.

It will sink because air is denser than helium.

It will rise because helium is less dense than air.

It will neither rise nor sink because air and helium are both gases.

26.

1 point

A barometer, which is often used to monitor the weather, is a device that measures air pressure. How could you use a barometer to measure your altitude as you climbed in the mountains?

You could tie a long string to the barometer, lower it to the ground below, then pull it back up and measure the string.

You could use a chart of altitude as a function of air pressure.

You could throw the barometer off the mountain measure its time of fall, and from that get your altitude.

You could trade the barometer to another mountain climber in return for him telling you your altitude.

27.

1 point

Why does a relatively modest narrowing of the coronary arteries, the blood vessels supplying blood to the heart, cause a dramatic drop in the amount of blood flowing through them?

The rate at which blood flows is proportional to the diameter of the blood vessel to the third power.

The rate at which blood flows is inversely proportional to the diameter of the blood vessel.

The rate at which blood flows is proportional to the diameter of the blood vessel to the fourth power

The rate at which blood flows is proportional to the diameter of the blood vessel squared.

28.

1 point

Why does hot maple syrup pour more easily than cold maple syrup?

Its viscosity is lower at higher temperatures.

Its Reynolds number decreases at higher temperatures.

Its viscosity is higher at higher temperatures.

Its Reynolds number increases at higher temperatures.

29.

1 point

A marshmallow is filled with air bubbles. Why does a marshmallow puff up when you toast it?

The heat makes the marshmallow expand.

The air in the bubbles gets warm and expands.

A chemical reaction occurs between the marshmallow and the air.

The air in the bubbles gets warm and thus its density increases.

30.

1 point

Water settles to the bottom of a tank of gasoline. Which takes up more space: 1 kg of water or 1 kg of gasoline?

1 kg of water because water is less dense than gasoline.

1 kg of gasoline because gasoline is less dense than water.

1 kg of gasoline because gasoline is more dense than water.

1 kg of water because water is more dense than gasoline.