1. The problem statement, all variables and given/known data when powder or granular solids are piled up. the powder forms a conical pile. the edge of the pile reaches a certain maximum angle with the horizontal, called the angle or repose. A) a pile of coal is found to have an angle of repose of 38% what is the relationship between height of the pile and its radius. i got that bit: h=r*Tan a h= height, r=radius a= Angle of repose B)if a conveyor belt pours the coal onto the pile at a rate of 0.3m^3/min, at what rate is the radius increasing when the radius is 1.7m i think i might have to derive the equaiton but i really dont know. i think i need the formula for the area of cone but i dont know. if i did i wouldnt be posting here!