[Systems Engineering Teachers' Mailing List] RE: syseng Digest, Vol 28, Issue 12 Practice exam errors

[Robert Minato]

As the spool rotates and reels the winch wire in, speed will be constant
until the winch wire fills the first layer. When the wire starts the second
layer, the circumference will be longer (radius now increased by thickness
of wire). Speed will change each subsequent layer and torque will reduce.

The speed of the drum will not change; however, the speed at which the wire
is hauled in (that's what the question is asking) will change for each
layer.

PS. It's nice to see some discussion on this list. Keep it up.


Rob
-- 
Robert Minato
Technology Leader
Catholic College Wodonga
1 Bowman Crt
Wodonga 3690
02 6043 5546



On 30/10/07 2:05 PM, "Powell, Warren S" <powell.warren.s at edumail.vic.gov.au>
wrote:

> Paul,
> I also have notified them of the wrong answers and have had no reply.
> In regard to Q12 the speed will not change. Only the diameter of the drum will
> change due to the cable coming and going. The drum is spinning on an axis
> therefore the speed will not change. The torque might increase a little.
> Hope this helps.
> 
> ________________________________
> 
> From: syseng-bounces at edulists.com.au on behalf of Barton, Paul S
> Sent: Tue 10/30/2007 8:46 AM
> To: syseng at edulists.com.au
> Subject: RE: syseng Digest, Vol 28, Issue 12 Practice exam errors
> 
> 
> I have asked Lorraine Tran and Kristen Allen for an answer sheet to the
> practice exam questions over 4 months ago, as I also found problems with the
> practice exam. I agree with your findings on questions 6,7,11, question 9 I'll
> defer to your Knowledge. I also asked about question 5 (subjective), Question
> 3 (formula should be Force= pressure X area), section B q1,I found I needed 3
> pads and q12 the speed would be the minimum as the drum diameter increases so
> would the speed. I have also stated the correct vr ratio should be driven over
> driver if we are to comply with industry standards.
> 
> Paul Barton
> Technology teacher
> Dromana Secondary College
> 
> ________________________________
> 
> From: syseng-bounces at edulists.com.au on behalf of
> syseng-request at edulists.com.au
> Sent: Mon 10/29/2007 12:00 PM
> To: syseng at edulists.com.au
> Subject: syseng Digest, Vol 28, Issue 12
> 
> 
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> Today's Topics:
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>    1. Practice Exam errors (Robert Minato)
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> ----------------------------------------------------------------------
> 
> Message: 1
> Date: Mon, 29 Oct 2007 09:43:06 +1000
> From: Robert Minato <rminato at ccw.vic.edu.au>
> Subject: [Systems Engineering Teachers' Mailing List] Practice Exam
>         errors
> To: "syseng at edulists.com.au" <syseng at edulists.com.au>
> Message-ID: <7878124.6681193611395403.JavaMail.root at localhost>
> Content-Type: text/plain; charset=US-ASCII
> 
> Had a look at the new practice exam on the vcaa website. There are a few
> problems with it:
> 
> Section A
> Q6. Symbol for a voltage reg is not on the vcaa symbols list. Responses A, B
> and D all represent another component, so by default, Response C is left
> which must be the correct answer.
> Q7. 120 and 600 Ohm in parallel gives 100 Ohms. 12V/100Ohms = 120 mA. No
> correct response.
> Q11. Brown Green Yellow resistor is 150 kOhms. No correct response.
> 
> Section B
> Q9. The motor will only ever rotate in one direction. The back emf diode
> will be forward biased in one switch position effectively shorting across
> the motor. [Depending on the current supply and diode rating, the diode may
> burn-out, in which case the motor will then work in the second direction.
> Back emf diodes normally used when other components (eg transistor) are in
> circuit to prevent damage.]
> 
> Formula sheet
> The resistor colour code needs a multiplier column. Unless a great deal of
> time has been spent with the code, most students would nave some trouble
> with the multiplier. Probably explains the confusion with Section A Q11.
> 
> Rob
> 
> 
> --
> Robert Minato
> Technology Leader
> Catholic College Wodonga
> 1 Bowman Crt
> Wodonga 3690
> 02 6043 5546
> 
> 
> 
> 
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> End of syseng Digest, Vol 28, Issue 12
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