Student Doctor Network Forums physics help please (2 q's)
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 01-17-2007, 08:41 AM #1 Member   Join Date: Jan 2006 Posts: 1,292 physics help please (2 q's) SDN Members don't see this ad. (About Ads) 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
 01-17-2007, 09:05 AM #2 Member     Join Date: Mar 2002 Posts: 294 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.
 01-17-2007, 09:10 AM #3 Member   Join Date: Jan 2006 Posts: 1,292 these are not mcat q's just hmwk i have to do
 01-17-2007, 09:27 AM #4 Member     Join Date: Mar 2002 Posts: 294 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.
01-17-2007, 09:44 AM   #5
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Quote:
 Originally Posted by HippocratesX 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.
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.

 01-17-2007, 11:52 AM #6 This space is for sale     Status: Pre-Medical Join Date: Feb 2006 Location: NY Posts: 3,665 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.

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