# Homework Help: How many ways can I flip switch positions to make the motor stop

1. May 22, 2012

### Femme_physics

Last edited by a moderator: May 6, 2017
2. May 22, 2012

### I like Serena

There is a total of 16 configurations and only a few of them will let the engine turn.

But there are more configurations than you mentioned.

Last edited: May 22, 2012
3. May 22, 2012

### Ouabache

Hi FP !
Perhaps it would be a good starting point to determine which positions will allow the motor to start.
(also ILS alluded to this)
Once you have that, it should be clearer which positions will shut the motor off.

hmmm i wonder where ILS got 16 configs? [hint 2 positions, 4 switches]. Perhaps a useful way to represent this problem is with a binary table with switch & position as inputs and output: "motor ON/OFF"

Last edited: May 22, 2012
4. May 23, 2012

### Femme_physics

Oops, you're right!

Fair enough

http://img842.imageshack.us/img842/5904/motormode.jpg [Broken]

How's that? :)

Last edited by a moderator: May 6, 2017
5. May 23, 2012

### I like Serena

I like the table. :)

Let's take a look at the first line where you say the motor is turning.
That would be with switches 1,2,3 in position 1, and with switch 4 in position 2.

Can you say how the currents will flow?

Last edited by a moderator: May 6, 2017
6. May 23, 2012

### Femme_physics

Last edited by a moderator: May 6, 2017
7. May 23, 2012

### I like Serena

Nice drawing. :)

How about the current through switch 1?
Which current will be bigger, the current through switch 1 or the current through switch 2?

8. May 23, 2012

### Femme_physics

Well the current through the first switch meets no resistance, therefor it will be much higher. Hmm. Short circuit eh?

9. May 23, 2012

### I like Serena

Yep. Short circuit.
I don't think there will be current left for the motor to turn. ;)

(Poor carton board men that are frying.)

10. May 23, 2012

### Femme_physics

I agree. :) Is that the only blunder I made?

11. May 23, 2012

### I like Serena

Well, I haven't checked out all your switch-combinations.
How many will be left with the motor turning if you remove all short circuits?

12. May 23, 2012

### Femme_physics

Last edited by a moderator: May 6, 2017
13. May 23, 2012

### I like Serena

And another one bites the dust! ;)
All correct now.

14. May 23, 2012

### Ouabache

Good Job!!
As you are learning in solving such questions, analyzing how a circuit functions is most important.
Once you've determined that, the rest follows more easily.

Your encoding is easy enough to follow. Another way to encode your table is in standard binary.
for example: on the input side, position1=0, position2=1. output side: motor off = 0, motor on = 1.

Last edited: May 23, 2012