1. The question This question is about the design of a car seat belt. The seat belt restraints a passenger when the car is involved in an accident. Use definitions of stress and strain to show that stress x strain has the same units as energy stored per unit volume of seat belt. 2. Relevant equations Deriving question hence no specific equation required. 3. The attempt at a solution stress x strain = force/area x extension\length = Nm/m^3 = N/m^2 = Nm^(-2) energy stored per unit volume of seat belt = J/m^3 4. The problem occurring I am not getting the same unit so it's contradicting the question. Can I have help as to where I have gone wrong. Thanks in advance.