Which statements describe the motion of a planet according to Kepler’s second law? Check all that apply. 1. The speed of a planet varies as it moves in its orbit.
2. The speed of a planet is constant as it moves in its orbit.
3. A planet travels the same distance along its orbit in equal units of time.
4. A planet sweeps out an equal area in equal units of time.
5. A planet’s orbit is a circle centered on the Sun.
6. A planet’s orbit is an ellipse with the Sun at one focus.

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