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Physics Help Please!?
The professor openly admitted this problem was probably way too hard but we're supposed to solve it nevertheless. Any help here? He said to use work equations.
From what maximum height can a 74 person jump without breaking the lower leg bone of either leg? Ignore air resistance and assume the CM of the person moves a distance of 0.58 from the standing to the seated position (that is, in breaking the fall). Assume the breaking strength (force per unit area) of bone is , and its smallest cross-sectional area is . [Hint: Do not try this experimentally.]
1 Answer
- 10 years agoFavorite Answer
:/ I can tell you what to do, but you won't get a solution without numbers.
1. Multiply the breaking strength by the cross-sectional area. This will give you the maximum force the bone can withstand.
2. Take this value and enter it in the equation Work=Force x distance. This will tell you the work it takes to bring the person to rest. The distance of course is the .58 meters, because that's how long the force will be applied.
3. Work = Difference in Kinetic Energy, so you can take the value from step two and plug it in for W. Then use the equation for KE on the other side. You will end up with [#]=1/2 mass x velocity^2, with # being the value from step 2. Plug in your guy's mass of 74 kg, and solve for velocity. Almost done!
4. Take this velocity and use it for the final speed in a kinematic equation. I would use FinalSpeed^2 = InitialSpeed^2 + 2acceleration xdifference in position. Our final speed will be the result of step 3, the initial speed 0 m/s (assuming the guy steps off a platform or something) and the acceleration that of gravity, which is 9.8 m/s^2. Solve for the position and you have your answer!
Numeric example:
1. F= breaking strength x cross-sectional area
2. W=Fd
W= # x .58 m
3. W=1/2mv^2
#=.5(74)v^2
v=#
4. vf^2=vi^2+2a(x)
#^2=0+2(9.8)(x)
I know it's kinda confusing but it's hard w/out #'s... hope this helps
