Physics 1050 Final Exam

You are a deep sea diver and are carrying out pressure tests on your air tanks, which are required by inspection rules. A gas cylinder is filled with a gas at a temperature of 300 K and pressure 200000 Pa. The temperature of the gas is then raised to 400 K. What is the new pressure?

266,667 Pa

An ideally efficient heater adds 1100 J of heat to a warm room. How much work does it perform if it removes 1400 J of energy from the outdoors?

300 J

Suppose you push a 50 kg box 10 m up a frictionless incline that is inclined 6º with respect to the horizontal. What is the change in potential energy for the box?

500 J W = Fd

Suppose you are standing at the top of a building and you measure your weight to be 728 N. At that location, how much force is the Earth exerting on you, if any?

728 N

Why must the surface of a hammer be very hard and stiff for it to drive a nail into wood?

A stiffer surface flexes little on impact, which reduces the time required to accelerate the nail, which means that the force on the nail is greater.

You're cutting wood with a handsaw. You have to push the saw away from you as it moves away from you and pull the saw toward you as it moves toward you. When are you doing positive work on the saw?

Both while pushing and pulling.

People falling from a high diving board feel weightless. Has gravity stopped exerting a force on them? If not, why don't they feel it?

Gravity still exerts a force on them, but they don't feel it because their apparent weight has become zero.

Spacecraft in low earth orbit take about 90 minutes to circle the earth. Why can't they be made to orbit the earth in half that amount of time?

Halving the time would require an orbit traveling inside the earth.

If you put a warm bottle of wine in a container of ice water, the wine will cool but the ice water won't become warmer. Where is the wine's thermal energy going?

It melts some of the ice.

Suppose the time it takes for the moon to rotate doubles. By what factor will its rotational kinetic energy change?

It will decrease to 1/4 its original value.

How would a Frisbee fly on the airless moon?

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

The surface of the moon is exposed to full solar radiation because it has no atmosphere. Why then does the moon not heat up endlessly until it disintegrates?

Its temperature rises until it is able to radiate heat away into space as fast as it arrives from the sun.

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 the back of the ball there should be

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

When a fish is floating in water near the bottom of a lake, what forces act on it, and what is the net force?

Lift and weight, for a net force zero.

Tightrope walkers often use long poles for balance. Although the poles don't weigh much, they can exert substantial balanced torques on the walkers to keep them from tipping and falling off the ropes. Why are the poles so long?

Longer poles mean larger torques.

A common feature of a pair of pliers is a location for cutting wires, bolts, or nails. Why is it so important that this cutting location is very near the pliers' pivot?

Small lever arm from the pivot to the cutting location produces a large force.

A thermoelectric cooler is a type of heat pump that uses electric power to move heat against its natural direction of flow. In other words, it takes energy from a system and transfers it to another system which is set at a higher temperature. In such a heat pump

The cooler requires power input because the flow of heat from a cool region to a warm region alone would decrease the entropy (disorder) of the system.

A hammer's weight is directed downward, so how can a hammer push a nail upward into the ceiling?

The force stopping the hammer is downward so the force on the nail is upward.

Why does fuzz on a tennis ball help it travel farther when hit?

The fuzz disrupts the boundary layer, causing turbulence everywhere around the ball.

A doctor can study a patient's circulation by imaging the infrared light emitted by the patient's skin. Tissue with poor blood flow is relatively cool. What changes in the infrared emission would indicate such a cool spot?

The infrared emissions from the cool spot would be less bright and shifted toward longer wavelengths.

If the momentum of a firework shell is conserved during an explosion, what can be said about the momentum of each of the various fragments of the system before and after it explodes?

The momentum of each individual part of the firework shell is not necessarily conserved.

Soil heats up much faster than water when the two are exposed to sunlight. Use that fact and your understanding of heat transfer to predict which way the wind will blow near the surface of the earth as the sun rises near the seashore.

The surface wind will blow from the land toward the water.

A toy top spins for a very long time on its sharp point. Why does it take so long for friction to slow the top's rotation?

The top's point is very small, so the torque generated by friction is small.

When you turn while riding a bike, you must lean in the direction of a turn or risk falling over. If you lean left as you turn left, why don't you fall over to the left?

The torque produced by leaning left counterbalances the torque produced by the ground on the tires, so there is no net torque about the center of mass.

For an object that sinks in a fluid,

The weight of fluid displaced is less than its weight.

Suppose an ice skater is moving on the surface of a frozen lake at constant velocity. What is true about the external (outside) forces acting on the skater?

There could be some but they all cancel out.

True or false? The pressure on a fluid in a pipe will be lower in regions where the fluid moves faster.

This is only true for pipes oriented horizontally.

Suppose you are riding on a merry-go-round and you move out to the edge. Does the angular velocity of the system decrease? If so, why?

Yes, angular momentum is conserved and the moment of inertia increased.

While hanging a picture, you accidentally dent the wall with a hammer. Did the hammer do work on the wall?

Yes, it does positive work on the wall.

Suppose you had a very long straw that could reach from a cup of water on the ground level to the top of a very tall building. When you suck on the straw in order to bring water up,

You could bring water up to only a certain height in the straw because the atmosphere pushes down on the surface of the water by a given amount.

If you blow across the top of a half full bottle of soda you can produce a clear tone. If you take a drink of soda to reduce the amount of liquid in the bottle and try this again the pitch of the sound produced will

decrease

At the moment your car reaches the top in a smoothly turning circular Ferris wheel, which way are you accelerating?

downward

You have watched one too many old cartoons and decide to drive around town with a giant spring that is 4 m long and attached to the front of your car. You decide to help a semi truck that is stuck and try to push them with your car. You take a running start, and when you contact the truck the spring in your compresses 3 m. During which portion of the compression did you do the least work on the spring?

during the first meter of compression

For momentum to be conserved in a system it must

experience no net external force

In a car engine, the compression stroke involves the piston compressing the air/gas mixture so rapidly that virtually no heat loss can occur. In the compression stroke, the air/gas mixture

heats because work is being done on the air/gas mixture

The neighborhood children are playing and one has lost a pocketful of change. As a result they all decide to do a close inspection of the sidewalk. They notice that there are gaps in between the sidewalk filled with a felt like material. These gaps will prevent

high stress due to thermal expansion

Some climatologists say that our climate could be warm enough to melt the polar ice caps, sending the resulting water down towards the equator. If this were to happen, the length of the day would

increase due to angular momentum conservation

Suppose your car is traveling at a certain speed on a very slick road. All of a sudden you step on the accelerator and the back wheels begin to spin but the car remains at the same speed. The total kinetic energy of the car

increases because of the increased rotation of the tires

The "strokes", or "cycles" in a four stroke engine are

induction, compression, power, exhaust

You stop for a cappuccino at a coffee shop and notice that the tiny white bubbles of steamed milk remain on the surface of the coffee. These air-filled bubbles stay where they are, rather than descending into the coffee or rising into the air, because they are

less dense than the coffee but more dense than the air above the coffee

A wave travels across the water on a lake, heading northward. As the result of this wave's passage, water on the surface of the lake

moves back and forth but makes no overall movement

Suppose a water wave strikes a very large solid barrier, such as a cliff. The wave will redirect its motion through

reflection

You are on your honeymoon but the only thing you can notice is that waves which strike the shore do so traveling directly towards it. This is an effect of

refraction, because as the water shallows the waves are bent so as to travel more directly towards the shore

Suppose you are at a stop light and realize that an important antique physics textbook sale ends in five minutes. Naturally, you start off very rapidly. To you, some papers on the dashboard fly straight backwards. To an observer they

remained where they were

A popular classroom demonstration is to place a gas can on a burner and boil water in it. Left unchecked this has the potential to be a very boring demo. However the can is removed from the flame and the lid is screwed on tightly. After it cools down the can will

shrivel up, since the atmosphere exerts more force on the can as it cools

Suppose you have an aquarium and into the water you have dropped a solid plastic decoration and a rock - about the same volume as the plastic one but twice as dense. Both are totally submerged in the water and falling towards the aquarium's bottom. The buoyant force on the plastic object is about ________ that on the rock. Assume the density of plastic is 60 kg/m^3 and that the density of the rock is 2,500 kg/m^3.

the same as

You accidentally miss the doorway and run into the wall. You suddenly experience a backward force that is several times larger than your weight. The reason this force is so large is

your deceleration is huge as you stop so suddenly

You are staring at a non-rotating wind turbine and all of a sudden the wind comes up and makes the turbine start rotating clockwise. The net force that causes translational motion is ________ and the torque causing the turbine to rotate is ________.

zero; away from you