VISUAL PHYSICS ONLINE

4.1 ELECTRICITY

P41 010

The starter motor of a car is turning too slowly, and the mechanic must decide whether to replace the starter motor, the cable or battery. The manufacture’s manual says that the 12.0 V battery can have no more than 0.020 resistance, the cable no more than 0.040 , and the motor no more than 0.200 . The mechanic turns the starter motor and measures 11.4 V across the battery, 3.0 V across the cable and a current of 50 A. Which part is defective? The reasons for your answer must be clearly stated.

View solution below only after you have completed answering the question. The solution is not in a form that you would answer in an examination. The answers are often in more detail to help improve your appreciation and understanding of the physics.

Solution

Knowledge

Circuit diagram

Battery

Starter Motor

Cable

So, the cable would need to be replaced.