(a) What is the average useful power output (in W) of a person who does 6.80 x 106 ] of useful work in 8.40 h? (b) Working at this rate, how long (in s) will it take this person to lift 1500 kg of bricks 1.40 m to a platform? (Work done to lift his body can be omitted because it is not considered useful output here.) 8046.42 S Because it can go from rest to 17.6 m/s (about 39 mi/h) in 2.6 s, one of the fastest-accelerating animals is the cheetah. If its mass is 50.0 kg, determine the average power developed by the cheetah during the acceleration phase of its motion. Express your answer in the following units. (a) watts Can you write an expression for the average power of the cheetah in terms of the work done by the cheetah and the time over which this work is done? How does the work done by the cheetah compare to its change in kinetic energy? Can you write an expression for the change in kinetic energy of the cheetah in terms of its final and initial speed? W (b) horsepower Can you find the conversion factor for watts to horsepower? hp Shoveling snow can be extremely taxing since the arms have such a low efficiency in this activity. Suppose a person shoveling a sidewalk metabolizes food at the rate of 850 W. (The efficiency of a person shoveling is 3%.) (a) What is her useful power output (in W)? 25.5 W (b) How long (in s) will it take her to lift 3,300 kg of snow 1.20 m? (This could be the amount of heavy snow on 60.0 ft of sidewalk.) 1577 What is the relationship between power output, work output and the time needed to do the work? Can you express the power output in terms of the efficiency and the power input? Can you express the work output in term of the change in gravitational potential energy of the snow? s (c) How much waste heat (in J) will she generate in the process? 1218009 Can you find an expression relating the heat generated to the work output? J