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(a) What is the average useful power output of a person who does 6.00 × 10^6 J of useful work in 8.00 h?

a) 250 W
b) 312.5 W
c) 375 W
d) 500 W

(b) Working at this rate, how long will it take this person to lift 2000 kg of bricks 1.50 m to a platform? (Work done to lift his body can be omitted because it is not considered useful output here.)
a) 12.5 s
b) 15.0 s
c) 18.0 s
d) 20.0 s

User Alina
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1 Answer

6 votes

Final answer:

The average useful power output is calculated using the work done over the time period. Based on the given values, the average power output would be 208.3 W, which does not match the provided options, suggesting a possible error in the question. Similarly, the calculation for the time to lift bricks also provides a result not in line with the given options.

Step-by-step explanation:

To calculate the average useful power output of a person, we use the formula:

Power = Work / Time

For the given values, that would be:

Power = 6.00 × 106 J / (8.00 h × 3600 s/h)

Power = 6.00 × 106 J / 28800 s

Power = 208.33 W

So the closest answer would be option b) 208.3 W, but this is not one of the choices provided, so there might be an error in the question or the choices given.

Next, to calculate how long it will take to lift 2000 kg of bricks 1.50 m, we would first have to calculate the work done, which is:

Work = Force × Distance

Since Force = mass × gravity,

Work = mass × gravity × Distance

Work = 2000 kg × 9.81 m/s2 × 1.50 m

Work = 29430 J

Now to find the time, we would use the same average power:

Time = Work / Power

Time = 29430 J / 208.33 W

Time = 141.22 s

Again, the answer does not align with the options provided, signaling an error in the question or given choices.

User James LT
by
7.7k points

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