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# physics help please (2 q's)

Discussion in 'MCAT Discussions' started by moto_za, Jan 17, 2007.

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1. ### moto_zaMember

Joined:
Jan 16, 2006
Messages:
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Question 1

During aerobic exercising, people often suffer injuries to knees and other joints due to HIGH ACCELERATIONS. When do these high accelerations occur?

Question 2

Estimate the acceleration you subject yourself to if you walk into a brick wall at normal walking speed.
(Make a reasonable estimate of your speed and of the time it takes you to come to a stop.)

thanks a bunch
2. ### HippocratesXMember

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Mar 22, 2002
Messages:
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These don't sound like legitimate MCAT physics questions to me? As long as you understand the reasoning behind acceleration and why it would cause damage to your joints if you were changing your velocity,say, for example from 50m/s to 0 m/s in a short time, ....then I wouldnt worry too much about what type of aerobic exercise or what normal walking speed is. These are not things you have to know for the MCAT, they are extraneous information that should be given to you in the passage.
3. ### moto_zaMember

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Jan 16, 2006
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these are not mcat q's just hmwk i have to do
4. ### HippocratesXMember

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Mar 22, 2002
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ok i see....well in that case, I would say that running can be an aerobic exercise, so when you stop quickly from a sprinting run, that does damage on your knees/joints and its also high acceleration (remember acceleration doesnt always mean speeding up), it can be acceleration when you're slowing down too, just in the opposite direction.

and as to number 2, i would just make up any number that sounds reasonable for walking speed and find the acceleration from (V-final - V-initial)/change in time. V-final is zero since the wall stops the person.
5. ### vincikaiSenior Member

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and if your body happen to bonce back after you walk into the wall. the accel excerted by the wall onto your body is actually a little more than that, it all depends how much you bonce lol.
6. ### FunkyThis space is for sale

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if you can make up how fast you're walking and the time it takes you to stop then just find out average acceleration(or in this case, deceleration) by (Vf-Vo)/t for question 2.

for question 1, you can just make up a scenario. One that comes to mind is an armbar. force is being applied to your elbow and your elbow can snap if the right amount of force is applied. correlate this to f=ma and there you have it.