Consider a situation in which a manufacturing assembly line is in operation. In this setup, a conveyor belt maintains a consistent speed of 2.5 m/s, while grains are deposited onto it from a hopper at a rate of 65 kg/s. If the conveyor belt experiences a friction force of 180 N, causing it to slow down, calculate the requisite output power in units of horsepower that the motor experiences over time. This analysis should commence from the instant the grains are initially deposited at t = 0 seconds and extend until 4.0 seconds after the grains commence sliding off the end of the 25-meter-long conveyor belt.