Question

when we jump on a heap of sand from a height we don't get hurt but on a floor from same height

Answer 1

It is due to resistive force applied by object
The resistive force of floor is higher then Sand
Or
In simple words the toughness of the object
One more thing is impact absorbed in sand is high then floor

Answer 2

When we jump on a heap of sand the time taken by your body to come to rest is larger so the force applied is not much impulsive so it hurts less but when you jump from same height on floor time taken is less and the force is more impulsive and you get hurt