The starting motor of a car is turning too slowly, and the mechanic has to decide whether to replace the motor, the ca- ble, or the battery.

Question

The starting motor of a car is turning too slowly, and the mechanic has to decide whether to replace the motor, the ca- ble, or the battery. The car’s manual says that the 12 V battery should have no more than 0.020 internal resistance, the motor no more than 0.200 resistance, and the cable no more than 0.040 resistance. The mechanic turns on the motor and mea- sures 11.4 V across the battery, 3.0 V across the cable, and a cur- rent of 50 A. Which part is defective?

a. the motor
b. the cable
c. the battery

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Thu Nguyệt 4 years 2021-07-28T20:14:31+00:00 1 Answers 35 views 0

Answers ( )

  1. lethu
    0
    2021-07-28T20:15:41+00:00
    Reply

    Answer:

    The cable is defective

    Explanation:

    First of all, let’s check if the battery is okay from the equation;

    Ir = ΔV

    Where;

    I is the current

    r is the internal resistance gotten

    ΔV is the difference in potential difference

    Thus;

    50(r) = (12 – 11.4)

    r = 0.6/50

    r = 0.012 ohms

    Now, thus value is less than the internal resistance of 0.02 ohms and thus it meets the requirement, so the battery is okay.

    Now, let’s check the cable from the equation;

    V = IR

    Where;

    V is voltage

    I is current

    R is resistance

    So,

    3 = 50(R)

    R = 3/50

    R = 0.06 ohms

    This is bigger than the maximum of 0.04 ohms required in the question. Thus, the cable is defective.

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