
#1
Jan2611, 11:23 AM

P: 30

[b]1. Estimation. “Crumple Zone”
a. Crumple zones in cars are designed to reduce the acceleration in a collision with a stationary object. Estimate a relation between the size of the crumple zone, the initial speed of the car, and the average stopping acceleration of the car’s occupants using dimensional analysis. Dimensional analysis does not start with the equations; it utilizes only the physical quantities and their dimensions to estimate. Part “b” is an actual estimate using some numbers. b. For a collision at 30 miles per hour, what is the minimum crumple zone size needed to keep accelerations below (a fatal) acceleration of 20g. How does this size compare to the length of a typical car (report this in percent)? Respond to this question it in one complete sentence? 2. Relevant equations p = (mass) * (velocity) impulse = (force) * (time) (change in momentum) = (impulse) p  p = (force) * (time) final initial m*v  m*v = (force) * (time) final initial Crumple Zone= L= length of 'crumple zone' 3. The attempt at a solution So for part A (which is what I need to know to find out part B) I am confused on how to get the length of the crumple zone into the equation and relate all of these terms. I would like a discussion on this question, but a nudge in the right direction would be helpful. I started by saying: vo= initial velocity and v1=0=final velocity. turning this m*v1  m*vo = (force) * (time) final initial but then v1 is taken out of the equation since final velocity is zero. How do I relate all the size of the crumple zone (L) to vo of the car and to the average stopping acceleration of a cars occupants? 



#2
Jan2611, 04:44 PM

P: 672

You were told explicitly not to involve any physics in the dimensional analysis. Throw out everything you know about collisions and use dimensional analysis.
Do you know how to perform dimensional analysis? If not, then refer to this text, scroll down to page 34 or so if you're familiar with the concept in its most general form. http://hubcap.clemson.edu/~daw/D_PHY...sisLecture.pdf This might prove simpler: http://www.efm.leeds.ac.uk/CIVE/CIVE...l_analysis.htm 


Register to reply 
Related Discussions  
In binary can we have a value with "deci" "centi" "mili" or more lower valued prefix?  Computers  14  
Help me Understand "Closed Under Addition" and "Closed Under Multiplication"  Calculus & Beyond Homework  2  
crumple zone using paper  Introductory Physics Homework  0  
Building a crumple zone  Introductory Physics Homework  5  
So, talk to me about the "Cambrian Explosion" por favor.  Biology  2 