(10%) Problem 9: Suppose a person does 1] x 106 J of useful work in 8.25 h. E g 50% Part (a) What is the average useful power output, in watts, of the person? D A 50% Part (b) Working at this rate, how long, in seconds, will it take this person to lift 1900 kg of bricks 1.6 m to a platform? (Work done to lift his body can be omitted because it is not considered useful output.) t=|| 7L9 456 173 -0