The manufacturer of a 1.5 v d flashlight battery says that the battery will deliver 9 ma for 42 continuous hours. during that time the voltage will drop from 1.5 v to 1.0 v. assume the drop in voltage is linear with time.
how much energy does the battery deliver in this 37h interval?

The illuminance of a surface varies inversely with the square of its distance from the light source. if the illuminance of a surface is 120 lumens per square meter when its distance from a certain light source is 6 meters, by how many meters should the distance of the surface from the source be increased to reduce its illuminance to 30 lumens per square meter?