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 - momentum. The formula \(J=\Delta p = F\Delta t\) (where \(J\) is impulse, \(\Delta p\) is change in momentum, \(F\) is force, and \(\Delta t\) is time interval). By increasing the time \(\Delta t\) over which the force acts (slowing vehicles down gradually), the force \(F\) (which causes damage and injury) is reduced. A rigid, unyielding structure (\(F\) is large as \(\Delta t\) is small) or directing cars into other obstacles (creates new collision points) is not effective. Creating a simple barrier does not address the energy - absorption aspect as well as gradually slowing the vehicle.

Answer:

C. by slowing vehicles down gradually