Tuesday
May 21, 2013

# Homework Help: physics

Posted by Sasha on Tuesday, October 27, 2009 at 10:23pm.

Highway safety engineers build soft barriers such as the one shown in Figure 3-21, so that cars hitting them will slow down at a safe rate. A person wearing a safety belt can withstand an acceleration of -3.0 102 m/s2. How thick should barriers be to safely stop a car that hits a barrier at 121 km/h?

• physics - brittany ad, Tuesday, October 27, 2009 at 11:08pm

almost 2 feet in width

• physics - digforbear, Wednesday, October 28, 2009 at 12:41am

first 121 km/h (1000m/1km)(1h/3600s) = 33.6 m/s

vf2 = vi2 + 2a(&Delta x)

&Delta x is what we want to solve for, it tells us the distance which we will compress the barrier so it needs to be atleast that thick

a is the max acceleration given which I don't really understand from what you've written (-3.0 102?)

vf is 0 because the car will stop

vi is 33.6 m/s

solving for &Delta x we get

[vf2 - vi2] / 2a = &Delta x

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