Question

how do energy - absorbing devices such as crash cushions work to provide roadside safety?
by creating a barrier that prevents cars from crashing into trees and utility poles
by directing cars into other obstacles
by slowing vehicles down gradually
by forming a rigid, unyielding structure that immediately stops vehicles

Explanation:

Energy - absorbing devices like crash cushions work based on the principle of impulse - force relationship. The formula \(F=\frac{\Delta p}{\Delta t}\) (where \(F\) is force, \(\Delta p\) is change in momentum, and \(\Delta t\) is time interval) shows that for a given change in momentum (\(\Delta p\)), increasing the time of impact (\(\Delta t\)) reduces the force (\(F\)). Crash cushions increase the time of impact by deforming gradually, which is equivalent to slowing vehicles down gradually.

Option 1: Creating a barrier that just prevents crashing (without energy - absorption) is not the function of energy - absorbing devices. They are not just simple barriers.
Option 2: Directing cars into other obstacles is not a safety - enhancing or energy - absorbing mechanism.
Option 4: A rigid, unyielding structure that immediately stops vehicles would result in a very large force (since \(\Delta t\) is very small in \(F = \frac{\Delta p}{\Delta t}\)), which is dangerous.

Answer:

by slowing vehicles down gradually