Jumping from greater height means that you achieve higher velocity before landing, hence there is a larger downward momentum at the time of landing. The moment the person lands, the momentum has to change to zero in an instant. Newton’s second law of motion states that the force applied is directly proportional to the rate of change of momentum. Since the amount of time taken to get rid of the momentum is the same in both cases, and you have more momentum to get rid of when you jump from a higher height, more force is required to bring you to rest if you jump from a higher height. This is the reason why we hurt ourselves when we jump from a higher height.