Solve Work-Energy Problem for Girl Cliff Diving

[DeepPatel]

Homework Statement

A girl is cliff diving. She jumps (assume from rest) from an 80 meter high cliff.

a) If her mass is 64 kg, and her body can only withstand a force of 11,000 N without breaking a bone, what is the minimum depth she must go into the water and not get hurt?

b) If we assume she goes 3.8 meters under the water, what force does her body feel?

Homework Equations

mgh+Fdcos(theta)=1/2mv²_f

m = 64kg, v_f = 0m/s F₁ = 11000N, h = 80m, d₂ = 3.8m, d₁ = ?, F₂ = ?

The Attempt at a Solution

a) I used the above equation to solve for d₂ and I got an answer of 4.65m as the depth.

b) I used the above equation to solve for F₂ and I got an answer of 13,473N as the force.

 

[haruspex]

That all looks right. But note the question assumes the force is constant in the water. That would not be true in practice.