The speed of a car is increased uniformly from 20. meters per second to 30. meters per second towards the right in 4.0 seconds. The magnitude of the car's average
acceleration in this 4.0-second interval is

A 13m/s2

B 2.5m/s2

C 10m/s2

D 0.40m/s2

Light from two different sources are incident upon the same side of a polarizing filter. light from one source is polarized with total intensity ip, while light from the other source is unpolarized with total intensity iu. as you rotate the polarizing filter through 360 degrees, the intensity of the transmitted light on the other side varies by a factor of 9. what is the relative intensity of the initial polarized source to the unpolarized source, or ip/iu?