Questions on Power

[pnoybballin]

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1. If an electrical generator plant increases its daily amount of output energy by 100%, the plant's average output power increases by:

A. 25%
B. 50%
C. 100%
D. 200%

The answer is C but shouldn't it be D?

2. It is observed that the power output of a jet engine increases by 100%. Which of the following single changes could explain this?

A. The time over which the fuel was burned decreased by 100%.
B. The output force of the engine increased by 100%.
C. The distance over which the engine was running increased by 200%.
D. The distance over which the engine was running decreased by 50%.

The answer is B but wouldn't A be a legitimate answer as well?

Thanks a lot everyone.

 

[pnoybballin]

bump

 

[thebillsfan]

a) just use common sense and think about that again. doubling something means increasing it by 100%

b) if the fuel decreased by 100% that would mean zero fuel. probably it would have to decrease by 50%.

 

[pnoybballin]

Correct me if I am wrong, but for the first problem my guess is that the output power would be increased to 200% but since the question is asking for average output power, you would divide that by 2 and thus it is 100%. Am I right?

For the second problem, P = ΔW / Δt so since P and Δt are inversely proportional, wouldn't a 100% decrease in Δt result in a 100% in P?

 

[Hemichordate]

Correct me if I am wrong, but for the first problem my guess is that the output power would be increased to 200% but since the question is asking for average output power, you would divide that by 2 and thus it is 100%. Am I right?

For the second problem, P = ΔW / Δt so since P and Δt are inversely proportional, wouldn't a 100% decrease in Δt result in a 100% in P?

For the first problem, if you look at it that way, wouldn't it be 50%?
If x is the normal output and 2x is the output after 100%, then (x+2x)/2 = 1.5x, which is 50% greater than the original output, thus B.

 

[thebillsfan]

hemi ive been dying to know what this "bankai" thing means on your signature. ive seen it all summer

 

[DrBO]

1) increasing something by 100% is like multiplying it by 2. So if you look at the formula Power=Work(energy)/time, if you multiply work by 2, the total power will increase by the same factor. Thus power increases by 100%.

Also, I=work/time is the equation for average power because you are taking the total amount of work done and dividing it by the time it took to do the work.

2) This can be explained logically. Both A and B are mathematically correct when using formulas. Yet if you decrease time by 100% you are making time equal to zero. You cannot divide by zero. Thus, B is the only possible answer.