Can you help explain these surprisingly different findings?

Question:

A 75-year old woman and her 9-year old granddaughter were in a train crash in which both sustained trauma to the chest while seated next to each other. X-rays showed that the grandmother had several fractured ribs, while her granddaughter had none. Can you help explain these surprisingly different findings...

Answers:
Well, age for one. Many women experience osteoporosis in old age which permits easy bone fracturing. Also, with the young girl, her body can take much more trauma simply due to her age and since than her septuagenarian grandmother.

This all, of course, is dependent on where and how they were sitting when the train crashed as well as who encountered more impact because of those factors.

The 75 year old womans bones are 75 years old. Hardly any 75 year old women DON'T have osteoporosis.
Kids bounce pretty good most of the time.

Due to age the grandmother's bones may have been more brittle, therefore more prone to breaking.

this is a relatively simple concept. would you rather have a pillow fight or a bag of cement fight. the bag of cement moving at the same speed as the pillow would hurt more because it has more mass. The woman and the grand daughter are traveling at the same speed on the train but when the train suddenly stops (crash) the woman hits the seat in front with more force because she weighs more.

Can you help explain these surprisingly different findings?

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