# Pressure problem

1. Apr 13, 2008

### frenchy7322

states of matter problem, me =

Total cross-sectional area of a load-bearing calcified portion of 2 forearm bones is approx 2.4cm squared. During a car crash, the forearm is slammed against the dashboard. the arm comes to frest from intiial speed of 80 km/h in 5.0 ms. If arm has effective mass of 3.0 kg and bone material can withstand a max compressional stress of 16x10^7 Pa, is arm likely to withstand crash?

Not sure on which equation to use due to not really getting the conceptual side of the question, please help!

2. Apr 14, 2008

### dynamicsolo

The compressional stress is a pressure, which is a force per area. You have the cross-sectional area of the bones, so you need the force applied. You know the mass upon which the force is applied, so you need the acceleration. The average acceleration can be found from the information that the bones are brought to rest from an initial speed of 80 km/hr in 0.005 seconds. (You only care about the magnitude of this acceleration; it doesn't matter that the acceleration is negative.) Be careful about your units: everything should be converted to SI, since you want the pressure in Pascals.

How does the average pressure to which the bone is subjected during this deceleration compare to 1.6·10^8 Pa?