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May 06, 2024, 04:52:18 pm
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Author Topic: head rest  (Read 2097 times)  Share 

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vitir

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head rest
« on: December 16, 2009, 02:30:48 pm »
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will we ever get questions like this one from the jacaranda ook:

when a stationary car is hit from behind by another vehicle at moderate speed, headrests behind the ocupants reduce the likelihood of injury. explain in terms of newtons laws how they do this?

I have the answer. just want to know if it is test worthy or anything
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NE2000

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Re: head rest
« Reply #1 on: December 16, 2009, 02:34:30 pm »
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Yeah it is test worthy (as in SAC-worthy). The exam was very non-descriptive for unit 3 this year but unit 4 was very much reliant on descriptive answers so you never know it might be exam-worthy too.
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appianway

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Re: head rest
« Reply #2 on: December 16, 2009, 07:57:29 pm »
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It's a very standard question. Put it on your cheat sheet if you want.
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vitir

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Re: head rest
« Reply #3 on: December 17, 2009, 01:31:23 am »
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: / how do they expect us to relate it to human physiology....
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kakar0t

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Re: head rest
« Reply #4 on: December 17, 2009, 02:46:38 am »
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Out of curiosity what would be a sufficient answer for this question?
-When the stationary vehicle is hit from behind the stationary vehicle suddenly gains momentum (p=mv) bla bla bla headrest increases the time over which the forces on the occupants head act, therefore...?
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vitir

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Re: head rest
« Reply #5 on: December 17, 2009, 04:13:15 am »
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actually no, it's not sufficient.

that's why I found it really interesting...

they had an answer about the law of inertia!

I thought like you did....and then they went on to talk about how its located at your head position and nothing to keep it from coming at you with a constant velocity, so because its connected to your neck and there is assumed to be a seat, you will have an equal and opposite reaction with your spinal cord causing damage to your spine.

wtf
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kenhung123

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Re: head rest
« Reply #6 on: December 17, 2009, 02:55:31 pm »
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I think its trying to say the impact is spread over your back with is less than all the impact on your neck.
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Edmund

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Re: head rest
« Reply #7 on: December 17, 2009, 03:10:01 pm »
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Inertia is correct. An explanation something like this would be sufficient:

Initially, the car and the person is stationary. When the car is hit from behind, the car's velocity changes but the person still 'remains stationary'. The person will therefore feel a force acting backwards. This is due to inertia. The head rest prevents the persons head from going backwards and breaking :(
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kakar0t

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Re: head rest
« Reply #8 on: December 18, 2009, 12:54:01 am »
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That makes perfect sense!! Thanks
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