Question

why is a person hit harder when he falls on a hard floor than when he falls on sand from same height.

Answer 1

the easiest way to explain is because sand is softer. But in reality you are hitting the sand with the same amount of force of you hitting the hard floor. Since the sand has many different little sand pebbles and they move, you don't feel that much hurt because as you fall and hit the sand, the little grains of sand move increasing your time of impact. When you hit a hard floor nothing is there to cushion you. You just hit a hard floor. Sand is supportive and increases your time of impact so you don't feel all the force on your body like you would if you hit a hard floor.

Answer 2

When you fall on sand, it takes some time for you to come to rest as the sand particles move. But when you fall on hard floor, your momentum becomes zero suddenly. So the change in momentum takes more time in sand than in hard floor. As we know the force acting is equal to rate of change of momentum, which is less in sand than hard floor, the force acting is less in sands than hard floor.