Question

Why is person hit har when he falls on a concrete floor than when he falls on a heap of sand from the same height?

Answer 1

The force applied by the concrete floor is higher than the force applied by the heap of the sand as according to Newton's second law, the rate of change of momentum is directly proportional to force applied.

$\frac{p_f - p_i}{ t} = F$

Since, the change in momentum is same in both the cases (Sand and concrete wall), but the time taken by the body to come to rest is less on the concrete wall as compared to sand. Due to the less time, the magnitude of force increases. Hence, it leads to more injury during a fall on concrete wall as compared to heap of sand.