[Q]: I can use this background: In the wiring of a building, the wires carrying the current in and out are different and never touch directly. The charge passing through the circuit always passes through an appliance (which acts as a resistor) or through another resistor, which limits the amount of current that can flow through a circuit. Appliances are designed to keep current at a relatively low level for safety purposes. The appropriate voltage and resistance in a circuit keeps the current in control and keeps the circuit safe. It is possible, however, for something to happen that causes the wire bringing the current in to come into contact with either the wire carrying the current out or the ground wire, thus causing what is called a short circuit . In a short circuit, some or all of the resistance is cut out of the circuit allowing the voltage to push a huge current through the wires. Now, I have a new situation: Greg is an electrical engineer. He works for an engineering firm that builds houses. Yesterday, Greg was checking two of the houses. He noticed that one of the houses had short circuit. He labeled that as case A. But the other house didn't have short circuit. He labeled that as case B. Answer this question please: In which case the incoming and outgoing current wires would not touch each other, case A or case B?
****
[A]: case B

[Q]: I can use this background: Look at the police car in Figure below . The sound waves from its siren travel outward in all directions. Because the car is racing forward (toward the right), the sound waves get bunched up in front of the car and spread out behind it. As the car approaches the person on the right (position B), the sound waves get closer and closer together. In other words, they have a higher frequency. This makes the siren sound higher in pitch. After the car speeds by the person on the left (position A), the sound waves get more and more spread out, so they have a lower frequency. This makes the siren sound lower in pitch. A change in the frequency of sound waves, relative to a stationary listener, when the source of the sound waves is moving is called the Doppler effect . You've probably experienced the Doppler effect yourself. The next time a vehicle with a siren races by, listen for the change in pitch. For an online animation of the Doppler effect, go to the URL below. Now, I have a new situation: John was sitting at point C near a railway track. Suddenly, he heard a train coming towards him from point A with constant sound of its horn. Eventually, it reached very close to him at point B. Then the train sped by him at point C where he was sitting, reaching point D after some time. Finally, it reached even farther from him at point E. Answer this question please: Which point would have lower frequency, point A or point B?
****
[A]: point A

[Q]: I can use this background: A screw is a simple machine that consists of an inclined plane wrapped around a central cylinder. No doubt you are familiar with screws like the wood screw in the left-hand side of the Figure below . The cap of the bottle pictured on the right is another example of a screw. Screws move objects to a greater depth (or higher elevation) by increasing the force applied to the screw. Many screws are used to hold things together, such as two pieces of wood or a screw cap and bottle. When you use a screw, you apply force to turn the inclined plane. The screw, in turn, applies greater force to the object, such as the wood or bottle top. You can watch an animation of a turning screw at the following URL. Now, I have a new situation: At a new years party Mary brought an expensive bottle of champagne for the host. Just before midnight she goes and finds a corkscrew to open the bottle. She places the corkscrew on the cork and begins twisting it, making the corkscrew push itself into the cork so she can open the bottle easier. Answer this question please: Will the force applied to the corkscrew's inclined plane have increased or decreased after Mary finishes twisting it?
****
[A]: increased

[Q]: I can use this background: One result of air pollution is acid rain. Acid rain is precipitation with a low (acidic) pH. This rain can be very destructive to wildlife. When acid rain falls in forests, freshwater habitats, or soils, it can kill insects and aquatic life. It causes this damage because of its very low pH. Sulfur oxides and nitrogen oxides in the air both cause acid rain to form ( Figure below ). Sulfur oxides are chemicals that are released from coal-fired power plants. Nitrogen oxides are released from motor vehicle exhaust. Now, I have a new situation: Hydrologists studied two samples of rain water. Jim studied an acid rain sample from a nearby city, and Dan studied a sample of water from another town. Answer this question please: Which hydrologist learned more about air pollution?
****
[A]:
Jim