A person who jumps or falls and lands feet first upon a hard ground places a gre

Question

A person who jumps or falls and lands feet first upon a hard ground places a great stress on the long bones of the leg. The most vulnerable bone is the tibia and the stress on this bone will be greatest at the point where the cross-sectional area is least, just above the ankle. The tibia will fracture if a compression force of more than about 50,000 N is applied. If a person lands on both feet stiffly, without bending their knees, the distance over which they decelerate will be about 1 cm (corresponding to the compression of the bones and joints in the leg). Suppose a person with a mass m = 75 kg falls from rest and lands on both feet. Assuming that the person decelerates at a constant rate, what is the maximum height from which the person can land without breaking either of their tibia?

Explanation / Answer

Let the force applied be 50,000 N

acceleration = 2*50000/75 = 1333 m/s

v = sqrt(2*1333*0.01)

= 5.16 m/s

Now height of jump required to achieve this speed,

h = v^2 /2g

= 5.16^2 /(2*9.8)

= 1.36 m answer

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.