4. Earth and Venus are almost identical in size and smaller than the Sun), but Venus is located closer to the Sun. Which of the following statements must be true? O A Earth will have a wider penumbra than Venus
O B. Earth will have a shorter umbra than Venus
O C. Earth will have a longer umbra than Venus.
OD. The umbra and penumbra of Venus and Earth will have nearly the same length and shape.

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