## rate of increase of a radius and height of a cone

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!
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 A cone has a third of the volume of a cylinder with the same height and base. Can you find the volume of the cone with that?