I thought it was pretty amazing that the cell phone was able to stop the bullet. I was curious about how much force the cell phone exerted on the bullet and the deceleration experienced by the bullet.

In order to determine this, I made several assumptions. I found the average

**mass**of a bullet to be 200grains or**.01kg**. I also determined that the average muzzle**velocity**is 850ft/s or**259m/s**. The article stated that the robber shot at the clerk on his way out of the store, so I assumed that the bullet traveled 5m before hitting the clerk. A bullet traveling at 259m/s would travel 5m in**.02s.**
So, we have the following information:

m = .01kg

v0 = 259m/s

vF = 0m/s

t = .02s

We now have enough information to calculate the net force exerted on the bullet by the cell phone.

Force = change in momentum / time

change in momentum of bullet = mFvF - m0v0

=(.01kg)(0m/s) - (.01kg)(259m/s)

=-2.59kg m/s

Fcell phone = (-2.59kg m/s) / .02s

= -129.5N

Now that have calculated the net force, we can figure out the deceleration experienced by the bullet using:

F = ma

-129.5N = (.01kg)a

a = -12950m/s2

That's incredible!

source: http://www.nydailynews.com/news/national/clerk-cell-phone-stops-crook-bullet-article-1.1499126

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