Aconcrete pump of 120-cy/hr max. output is used to place 250 cy of concrete. it is supplied by 8 cy transit-mix trucks arriving to the site every 15 mins. barring interruptions how many hours will the operation require, considering 80% efficiency factor.

Completing the operation will require 9.765625 hours.

Explanation:

First, let's check which of the stages will be the process limitation:

Regarding the pump, it can perform up to 120 cy/h. The trucks will deliver 8 cy every 15 min, i.e., 32 cy/h, then this is the smaller capacity within the whole process.

Now, let's establish a simple relation:

Placement speed x Efficiency = Placed quantity / time,

solving for time. we have

at positions a, g kinetic energy is maximum.

at position d, potential energy is maximum.

+15-35=-20

going in opposite directions