How much current does the motor draw?

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The starter motor in an automobile has a resistance of 0.37 Ω and operates on 12 V with a back emf of 10 V. The current drawn at normal operating speed is calculated to be 5.4 A. For the current at half its final rotational speed, the correct approach involves halving the back emf, not the current. This clarification resolves the confusion regarding the incorrect answer provided by Mastering Physics. Understanding the relationship between voltage, current, and back emf is crucial for accurate calculations in motor operations.
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Homework Statement


The starter motor in an automobile has a resistance of 0.37 Ω in its armature windings. The motor operates on 12 V and has a back emf of 10 V when running at normal operating speed.
A)How much current does the motor draw at its operating speed?
B)How much current does the motor draw when running at half its final rotational speed?


Homework Equations


Eb=V-IR


The Attempt at a Solution


I found part A) to be 5.4 A. Our professor told of to divide this by two to get part B. Mastering Physics tells me that 2.7 A is a wrong answer. Is this a MP glitch or do I have the wrong info?
 
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Sarak said:

Homework Statement


The starter motor in an automobile has a resistance of 0.37 Ω in its armature windings. The motor operates on 12 V and has a back emf of 10 V when running at normal operating speed.
A)How much current does the motor draw at its operating speed?
B)How much current does the motor draw when running at half its final rotational speed?


Homework Equations


Eb=V-IR


The Attempt at a Solution


I found part A) to be 5.4 A. Our professor told of to divide this by two to get part B. Mastering Physics tells me that 2.7 A is a wrong answer. Is this a MP glitch or do I have the wrong info?
Oops, never mind. He meant take half of the back emf, not half the current.
 
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