An important news announcement is transmitted by radio waves to people who are 51 km away, sitting next to their radios, and by sound waves to people sitting across the newsroom, 3.6 m from the newscaster. Take the speed of sound in air to be 348 m/s. What is the difference in time that the message is received

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