# Design of an automobile bumper

1. Sep 18, 2010

### James22

1. The problem statement, all variables and given/known data
I have posted the assignment hand out. The weight of the car will be 3702lbs.

2. Relevant equations

3. The attempt at a solution

Right now I am overwhelmed with this project, I am not really sure where to start. Here is my thoughts on where to start.

The weight of the car will be 3702lbs. I think I need to find the kinetic energy of the automobile traveling at 5 mi/h. Now knowing the kinetic energy, would the next step be to decide upon the number of springs and their coefficient needed to stop the auto in 3" or slightly more?

Thank you in advance and sorry if this seems elementary. Dynamics related work doesn't come easy to me to say the least.
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

#### Attached Files:

• ###### bumperassignment.JPG
File size:
71.4 KB
Views:
69
2. Sep 19, 2010

### James22

I worked on this project some more and calculated the kinetic energy as;

E=1/2 mv^2
0.5 x (3702/32.2) x 7.33ft/s^2 = 3091.38 ft-lb

I have chosen to use a 6" crumple zone and 4 springs to absorb the impact.

This is where I run into trouble trying to get my head around the concept.

I know for the spring
U=0.5*k*s^2

where;
k = Spring co-efficient
s = spring displacement

Since I am trying to stop the car in 6" do I have to treat the kinetic energy as double? Then divide it over the 4 springs that I will be using to stop the car?

Thanks,
Kyle