Final answer:
To calculate the average useful power output, divide the work done by the total time in seconds. The average power output is 178.57 W. Given this power, it would take the person 130.63 seconds to lift 1700 kg of bricks 1.40 m to a platform.
Step-by-step explanation:
The average useful power output of a person who does 5.40 × 106 J of useful work in 8.40 hours can be found by dividing the total work done by the total time in seconds. First, convert 8.40 hours to seconds: 8.40 hours × 3600 seconds/hour = 30240 seconds. Then divide the total work by the total time: 5.40 × 106 J / 30240 s = 178.57 W.
To find out how long it will take to lift 1700 kg of bricks 1.40 m, we need to calculate the work required by using the equation Work = force × distance. The force needed to lift the bricks is equivalent to their weight, which is the mass multiplied by the acceleration due to gravity (9.8 m/s2): Force = 1700 kg × 9.8 m/s2 = 16660 N. So the work done in lifting the bricks is 16660 N × 1.40 m = 23324 J.
Knowing the person's power output, we can find out how long it will take to do this work: Time = Work / Power = 23324 J / 178.57 W = 130.63 seconds.