Physics Review Question Unit: electricity and magnetism Year: 1992 Question#: 31 Question: An electric motor uses 15 amperes of current in a 440-volt circuit to raise an elevator weighing 11,000 Newtons. What is the average speed attained by the elevator? (1 ) 0.0027 m/s (2 ) 0.60 m/s (3 ) 27 m/s (4 ) 6,000 m/s What is this question really asking? Explanation by: Christine A [ Return to question menu ] Answer 1 0.0027 m/s INCORRECT When solving a problem such as this, always write out everything you know: I=15 Amperes V=440 Volts F=11,000 Newtons Now, looking at the information you have, the best formulas to use will be two variations on the power formula: P=VI P=Fv Since all variations are equal, you can set the two variations equal to each other: VI=Fv Then, all that is left to do is to plug in your numbers and solve for the unknown variable: VI=Fv (15A)(440 V)=(11,000 N)(v) 6600 Watts=(11,000 N)(v) .6 m/s=v Thus, the average speed attained by the elevator is .6 m/s. This is not what is written for answer 1, so answer 1 must be incorrect. return to top Answer 2 0.6 m/s CORRECT When solving a problem such as this, always write out everything you know: I=15 Amperes V=440 Volts F=11,000 Newtons Now, looking at the information you have, the best formulas to use will be two variations on the power formula: P=VI P=Fv Since all variations are equal, you can set the two variations equal to each other: VI=Fv Then, all that is left to do is to plug in your numbers and solve for the unknown variable: VI=Fv (15A)(440 V)=(11,000 N)(v) 6600 Watts=(11,000 N)(v)
Answer 3 27 m/s INCORRECT When solving a problem such as this, always write out everything you know: I=15 Amperes V=440 Volts F=11,000 Newtons Now, looking at the information you have, the best formulas to use will be two variations on the power formula: P=VI P=Fv Since all variations are equal, you can set the two variations equal to each other: VI=Fv Then, all that is left to do is to plug in your numbers and solve for the unknown variable: VI=Fv (15A)(440 V)=(11,000 N)(v) 6600 Watts=(11,000 N)(v)
Answer 4 6,000 m/s INCORRECT When solving a problem such as this, always write out everything you know: I=15 Amperes V=440 Volts F=11,000 Newtons Now, looking at the information you have, the best formulas to use will be two variations on the power formula: P=VI P=Fv Since all variations are equal, you can set the two variations equal to each other: VI=Fv Then, all that is left to do is to plug in your numbers and solve for the unknown variable: VI=Fv (15A)(440 V)=(11,000 N)(v) 6600 Watts=(11,000 N)(v)
What's this question really asking? Do you know how to deal with power formulas and their applications? return to top |
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