physics

Atmospheric pressure is about 100000 Pa. At what depth in water does this pressure double?

10 m

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.

As the Reynolds number decreases

A) flow is becoming more laminar.

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.

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.

17. At what place in or near the jet engine is gas moving the fastest relative to the flying airplane?

B) In the plume of exhaust gas flowing out of the engine's outlet duct.

Suppose you have gotten a new job where you have to design balls that fly through the air with as little resistance as possible. You know that in front of the ball there is laminar flow, so in back of the ball there should be

C) Laminar flow, so the leading and trailing pressure environments are similar.

When a fish hovers over the bottom of a lake, what forces act on it, and what is the net force?

D) Lift and weight, for a net force zero.

The diameter of a pipe is halved while the pressure difference across the pipe remains the same. The volume flow rate of the pipe

D) decreases by a factor of 16

Suppose you are practicing baseball and throw the ball with a spin so that it moves forward and curves to the right. Now when the actual game takes place you are pitching into the wind. Please explain how you could alter your throw so as to make the ball take the same path.

Drag resistance is responsible for slowing down the ball and depends on the ball's air speed. Since there is a head wind the ball will have to overcome the extra pressure so you would throw it harder than before. But now the ball's speed in the air is faster so you will have to also spin it less because the amount of deflection due to spinning depends on the ball's air speed as well as the spin rate.

Suppose you are practicing baseball and throw the ball with a spin so that it moves forward and curves to the right. Now when the actual game takes place you are pitching with the wind behind you. Please explain how you could alter your throw so as to make the ball take the same path.

Drag resistance is responsible for slowing down the ball and depends on the ball's air speed. Since there is a tail wind the ball will be carried a bit farther, so you would not throw it so hard as before. But now the ball's speed in the air is slower so you will have to also spin it faster because the amount of deflection due to spinning depends on the ball's air speed as well as the spin rate.

Suppose you throw a party to recognize that your physics class is over for the semester. You are at a restaurant with your friends and you make the comment "Look at that quarter sitting at the bottom of the aquarium. I now can tell you that its apparent weight is zero because it is underwater and supported by a buoyant force equal to the weight of the water it displaces". If your instructor were along and correctly commented on the scientific accuracy of your comment, what would they say?

Indeed, the buoyant force in the quarter is equal to the weight of water it displaces. However its apparent weight is equal to its true weight minus the buoyant force and the two forces are not equal because the object sinks. It is not moving because the normal force is making up for the different between its weight and the smaller buoyant force

Lead sinkers actually float on the surface of liquid mercury. Which takes up more space: 1 kg of mercury or 1 kg of lead?

Lead

In old western movies, after having fired their guns people would blow across the end of their guns and smoke would come out the barrel. Please explain.

The Bernoulli Effect says that faster moving fluids exert lower pressure. Since the air is moving (probably even rapidly) over the end of the barrel of the gun but is stationary inside the barrel there is higher pressure inside and lower pressure outside, which pushes the smoke outward.

You are eating out at a restaurant. The waiter is your lab partner in physics class, so you play a trick on him. You place his tip in an upside down glass about ¾ full of water, which is affixed to the smooth table surface. Why does the water stay in the glass?

The key here is the tight seal between the glass and table. For the water to leave the glass, air must enter to displace the water. If no air is able to displace the water inside the glass, the water can't leave.

You are seated at a table in a Paris Café, contemplating life and watching the bubbles rise upward in your glass of carbonated water. You can think of many physical reasons why those carbon dioxide bubbles should rise upward through the water. Which of the follow observations is not true and therefore does not help explain why the bubbles rise in your Perrier?

The pressure inside a bubble is much less than the pressure in the water around it.

For an object that is neutrally buoyant in a fluid,

The weight of the fluid displaced equals the object's weight.

You are camping in the breathtaking mountains if Colorado. You spy an unopened diet soda can floating motionless below the surface of a lake. What is the direction and amount of force the water exerts on it?

Up, equal to the can's weight

Suppose you have a car tire that is almost flat. There is a large amount of tire surface in contact with the street. When you pump the tire up there is much less tire surface contacting the road. Please explain why the change in tire pressure caused such a difference.

We know that pressure is force per unit area. Whether the tire is flat or pumped up it needs to support the same force. Since the product of pressure and area must be constant, when the pressure is lower the area of the tire contacting the road must be larger. For the higher pressure case the area has to be lower. Believe it or not, you can estimate the weight of your car by summing up the product of tire pressure times area for all your tires.

One warm spring day you and some friends go to the beach at a nearby lake. You are tossing a soft, almost fully inflated beach ball around when someone accidentally knocks it into the lake. Although it is a warm day, the water is still very cold so nobody wants to retrieve the ball. You notice that the ball seems to have deflated somewhat after sitting in the water for a while. The contact with the cool water has caused the temperature of the air inside the ball to drop, resulting in

an increase in the density of the air inside the ball.

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

has less pressure than slower moving water.

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

higher than atmospheric and the water's speed is slower than in the stream.

A block of hardwood is floating easily on the surface of a lake. As a storm approaches, the density and pressure of the air above the lake begin to decrease. As a result of this decrease in air pressure and density, the block of wood

moves downward slightly and floats lower in the water.

The pressure gradient set up in water standing is a glass is an example of ________ ________ in pressure, while variations in pressure due to water flowing faster in the smaller parts of a pipe are a type of ________ ________ in pressure.

static variation; dynamic variation

You are riding in a hot air balloon. You have not used the burner for some time and the balloon begins to sink. Assuming that no air is allowed to leave or enter the balloon,

the average density of the balloon became greater than the surrounding air and the buoyant force on the balloon became less than its weight.

In a popular classroom demonstration, a cotton ball is placed in the bottom of a strong test tube. A plunger fits inside the tube and it makes an air - tight seal. It is then pushed down very rapidly, and the cotton flashes and burns. This happens because

when the air was compressed its temperature increased.