# Millman's Worksheet Question 9

Discussion in 'Feedback and Suggestions' started by JoeJester, Dec 16, 2012.

Apr 26, 2005
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2. ### Georacer Moderator

Nov 25, 2009
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Oh, Joe, why can't you just point out typos like everybody else!

First and foremost, that cars image is horrible; the numbers are illegible. I 'd say that's the first thing that should be fixed.

Now, about your remark, I could say that the exact calculations shouldn't necessarily be visible in the solutions, since it's the last exercise of the batch. But a detailed explanation isn't given in any of the problems above either. A complete solution should be given for at least one of them.

The resistance on the starting motor should also be noted on the picture.

Your solution of course is neat and comes with a very neat schematic, although newcomers to electronics may find it hard to read the values and interpret the terminal connections.

3. ### hgmjr Moderator

Jan 28, 2005
9,030
214
Joe,

I agree with Georacer that several of the problem variables contained in the diagram are pretty much unreadable.

What I believe has tripped you up is that the starter motor in the car that is providing the jump-start is being treated as a 15V voltage source rather than a 0.15 ohm resistance as you have interpreted it in your solution. The resulting current it provides is adding to the overall current delivered to the starter motor on the car that is being jump-started.

I ran the numbers with the interpretation that I have described above and the answer I obtained comes very close to the answers provided in the reveal.

Let me know if this helps you out.

hgmjr

4. ### Georacer Moderator

Nov 25, 2009
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1,266
Actually, the 0.15Ω for the starter motor isn't an assumption. It is given in the sentence below the picture in the exercise.

5. ### hgmjr Moderator

Jan 28, 2005
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True, but I think that statement only refers to the car being jump started. The other car labels the starter motor with the value 15V. The assumption being that the starter motor in the car being used to jump start the dead battery car is outputing a voltage.

hgmjr

6. ### JoeJester Thread Starter AAC Fanatic!

Apr 26, 2005
3,373
1,159
hgmjr,

I took it as a starter motor and not a source, since it was in the "same" physical position as the "dead" vehicles "starter" and the same icon. They clearly identified the "starter" in the dead vehicle. Why didn't they clearly identify the same icon in the working vehicle?

If the "starter motor" on the running vehicle is a 15 volt source, then the numbers agree with the reveal. A simple word like generator or alternator or whatever they are called in Europe, would have clearly identified the icon as something other than a "starter".

I agree with Georacer about that diagram. I enlarged it to 200% and it's still terrible.

Last edited: Dec 16, 2012
7. ### hgmjr Moderator

Jan 28, 2005
9,030
214
Yeah, Joe. I initially missed the 15V label and jumped to the same conclusion that you did. Then I took another look and the 15V label caught my eye. A quick run of the numbers was enough to convince me the 15V source was all that was needed to obtain the final result called out in the reveal.

hgmjr