Can Being in a crash at 30 MPH has the equivalent force of being dropped off a four story building?

Answer 1

NO,

Let's break it down into terms that are easily to calculate:

30mph = 13.4 m/s

A four-story building is ~ 12meters high. The speed (final velocity) something reaches when it drops off 12meters is:

Vf = sqrt(2AD - Vi) = sqrt(2*9.8*12 - 0) = 15.336 m/s

so driving 30mph and dropping 4 stories is about the same speed. (~15m/s)

However, when you hit the ground off a building, you have a sudden impact, which lasts ~1/50 of a second.

In a Car, they are designed to have a "crumple zone" which means the front of the car will actually crumple and spread the impact over a little more time like ~1/10 of a second.

The longer impact time of a car will actually lessen the equivalent force, whereas the sudden smacking of the ground is a higher equivalent force.

Let's assume you weight 75kg = 165lbs

Since F = mass*acceleration, normally you feel 75*9.8= 735N on your feet

The moment your car crashes is:

F = mass*∆Velocity/time = 75kg*15m/s / (1/10) = 11250N

convert to pounds: 11250N/4.45 = 2528lbs

The moment you hit the ground when falling is:

F = 75kg*15m/s / (1/50) = 56250N

converted to pounds: 56250N/4.45 = 12,640lbs.

SO really, falling 4stories is 5x worse than getting in a 30mph car crash.