2-33. A rock drill can be operated at three different operating speeds, each with a unique drilling rate (i.e., rate of production). The faster the dril operates, the sooner the bit wears out and must be replaced. Replacement bits cost $10.00 each and cannot be re-sharpened. The drill operator costs $30.00 per hour. (2.4)

a. Assuming one drilling cycle requires 96 linear feet of drilling, which speed results in the lowest drilling cost per foot? Please provide the drilling cost per foot for each speed. Speed Drilling Rate (ft/min) Bit Life at This Speed (min) A 2 10 B3 6 C4 3

b. Assume it takes an average of 30 minutes to load and blast the holes drilled in one drilling cycle. If it takes longer than 30 minutes to complete a drilling cycle, then the blasters must wait on the drill at a cost of $60.00 per hour. Using the data from Part

(a) and considering the possible penalty for making the blasters wait, which speed results in the lowest drilling cost per foot AND how much is this cost per foot?