Which statement best explains why running on a track with constant speed at 3m/s is not work but climbing a mountain at 1m/s is work? 1. At constant speed, change in the kinetic energy is zero but climbing a mountain produces change in the potential energy
2. At constant speed, change in the potential energy is zero, but climbing a mountain produces change in the kinetic energy.
3. At constant speed, change in the kinetic energy is finite, but climbing a mountain produces no change in the potential energy.
4. At constant speed, change in the potential energy is finite, but climbing a mountain produces no change in the kinetic energy.

Write the equation for momentum, first using symbols for the variables, then using words for the variables.

Agas initially at p1 = 1 bar and occupying a volume of 0.5 liter is compressed within a piston–cylinder assembly to a final pressure p2 = 4 bar. (a) if the relationship between pressure and volume during the compression is pv = constant, determine the volume, in liters, at a pressure of 3 bar. (b) repeat for a linear pressure–volume relationship between the same end states. reference

Search coils and credit cards. one practical way to measure magnetic field strength uses a small, closely wound coil called a search coil. the coil is initially held with its plane perpendicular to a magnetic field. the coil is then either quickly rotated a quarter-turn about a diameter or quickly pulled out of the field. (a) derive the equation relating the total charge q that flows through a search coil to the magnetic-field magnitude b. the search coil has n turns, each with area a, and the flux through the coil is decreased from its initial maximum value to zero in a time ∆t. the resistance of the coil is r, and the total charge is q = i∆t, where i is the average current induced by the change in flux. (b) in a credit card reader, the magnetic strip on the back of a credit card is rapidly “swiped” past a coil within the reader. explain, using the same ideas that underlie the operation of a search coil, how the reader can decode the information stored in the pattern of magnetization on the strip. (c) is it necessary that the credit card be “swiped” through the reader at exactly the right speed? why or why not?