A surprising demonstration involves dropping egg from a third-floor window so that the egg lands on a foam-rubber pad without breaking. If a 56-g egg falls (from rest) 12m, and the 5cm thick foam pad stops it in 6.25ms, by how much is the pad compressed? (NOte: assume constant upward acceleration as the egg compresses the foam-rubber pad)

Answer 1

Calculate the speed V = sqrt (2gH) of the egg when it hits the pad. I get 15.3 m/s. Multiply that by the mass M to get the momentum, MV = 0.856 kg m/s. The average upward force on the egg, Fav, multiplied by the time to bring it to a stop (6.25*10^-3 s) equals the momentum. Therefore Fav = 137 Newtons.
The compression equals the average velocity during deceleration, 7.65 m/s multiplied by the time of contact,6.25*10^-3 s. I get 4.8 cm, just a bit less than the thickness of the pad. A thinner pad would not have worked.