Apoint source of light illuminates an aperture 4.00m away. a 18.0 cm -wide bright patch of light appears on a screen 2.00m behind the aperture.
i have been trying to use the equation w=(2*wavelength*distance)/aperature width. however, i am not given wavelength and the type of light is not specified. also, does the source of light being 4.00m away from the aperature even matter?

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