A boy stands between two vertical walls and fires a rifle. Under what condition will he hear a single echo from both walls? Calculate the distance between the walls if the single echo is heard six seconds later.​

Cells in the nervous system have a potential difference of 70 mv across the cell membrane separating the interior of the cell from the extracellular fluid. this potential difference is maintained by ion pumps that move charged ions across the membrane. is this an emf? select the correct answer and explanation. 1)no. the ion pumps cannot separate charges; thus, they cannot create a potential difference. 2)yes. the ion pumps cannot separate charges, but they still can create a potential difference. 3)yes. the ion pumps can actively separate charge; thus, they can create a potential difference. 4)no. the ion pumps can separate charges, but they cannot create a potential difference.

Suppose two stars are located in region a of the h-r diagram shown in the figure below. star c appears much dimmer than star y as seen from earth. which star can be inferred to be nearer to earth and how do you know?

Match the words or actions and their definition. 1. the rate of doing work 2. a machine that changes motion 3. the force that is used to generate electricity 4. 550 foot-pounds per second 5. the force that makes things fall toward the earth 6. work in > work out 7. metric measurement of work 8. the product of force times distance water falling from a dam newton-meter gravity work windmill power the work principle 1 horsepower