Afarmer uses 3450 j of energy on a wheel and axle to lift a 15 kg bucket of water 20 m to the top of her well. what is the efficiency of the system?

Explain why electric current cannot exist if a current doesn't have a voltage source.

In an old-fashioned amusement park ride, passengers stand inside a 3.0-m-tall, 5.0-m-diameter hollow steel cylinder with their backs against the wall. the cylinder begins to rotate about a vertical axis. then the floor on which the passengers are standing suddenly drops away! if all goes well, the passengers will “stick” to the wall and not slide. clothing has a static coefficient of friction against steel in the range 0.60 to 1.0 and a kinetic coefficient in the range 0.40 to 0.70. part a what is the minimum rotational frequency, in rpm, for which the ride is safe? express your answer using two significant figures. f f = rpm

The dominant wavelength of energy emitted by the sun is