A student of mass 65kg takes 10s to run up a flight of stairs of 40 steps. if each step is 12cm high . Calculate the potential energy of the student at the maximum height take gravity to be 10m/s square.

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?