richnfg

Yeah! I was going to post them in the same bit but I didn't.

thats cool hey if you need my presentation I will be happy to send it to you it might be of some help!

Phew. I'm glad all my physics was correct and such. ok, I will keep to this equation then say afterwards that other materials can actually have an effect and also the fact that if you bend your knees etc. It is really only a rough calculation to show that you can actually do these things. I got the limit 200MPa from my AS Advancing Level Physics book. Im guessing that is right! Variables: 1st equation: v = final speed and u = starting speed a = acceleration due to gravity s = distance 2nd: a = acceleration t = time 3rd: f = force m = mass 4th: s = stress a = cross-sectional area

It was just a very rough number that my teacher told me to use (so i thought I should use that one!)...apart from that, is the way I got to an answer acceptable?

I am trying to calculate whether someone would break their leg when jumping off a 4m wall. Check this out and please comment on if it is correct. Thanks. Will I Break My Leg If I Jump Off This Wall? For the physics presentation I will be including a calculation to show whether someone will break their leg if they jump off a wall. I already know these certain figures: the boy weighs 65 kg and the wall is 4m high. This calculation will only be an estimate but should give a rough idea of how to go about working this out and we will have to go through a few equations to get to the tensile stress. First we should calculate the speed that the person is travelling at and we can achieve this by: v² = u²+2as v² = 0 + 2 x 10 x 4 v² = 80 v = 8.9m/s(2 s.f.) We can then take the speed to work out the acceleration from the full speed to hitting the ground (the acceleration is useful for working out force in the next equation). The change in speed is 8.9m/s because the final speed will be zero and the time it takes to change from 8.9m/s to zero when you hit the floor would be estimated at around 0.01 of a second. a = (v-u)/t a = 8.9/0.01 a = 890ms-² We can then take this acceleration and times it by the mass of the person to calculate the force at which is exerted on the person (the mass of the boy is 65kg remember): f = ma f = 65 x 890 f = 57850 N Finally, knowing the cross sectional area of the bone (roughly .28 m² as I calculated earlier) we can work out the tensile stress that is put onto the bone: s = f/a s = 57850/.28 s = 206607 Pa s = 206.607 MPa We said that the bone would require 200 MPa to break and in this case it would. THanks!"

Yep thanks!

I'm sorry, I could of searched Google. I needed a quick answer as I need it for my presentation tomorrow and I'm in a rush!

Is there a formula to work out the speed in this situation? A 65kg man jumps off a 2m high wall, could I find the speed from this (by time he hits the ground)? Thanks!

I'd just like to say thanks to Blike (for about the 1000th time ) because he was very helpful and so was the information he supplied.

Thanks, that is a big help! If anyone could post some figures about Young Modulus and Breaking Stress of bone that would be incredibly helpful.

I play guitar and bass and recently started learning piano!

Wow, sounds good!

Thanks Blike for the offer, I'll contact you! Wow, it sounds like it might be beyond my level or more towards a different area of the bone. Has it got anything about the strength of bones etc? (I'm not sure what fatigue crack propagation is ) Anything else would still be very useful! Thanks!

Before saying anything, sorry that my first post on this forum is looking for help. Thats not a good thing, I know. I do intend to post more. Anyway, for my A-level physics coursework I need to give a presentation on a material of my choice...most of the other people in my class got the easier materials / materials with more information on them - I'm stuck with human bones. Ok, any links to information or websites would be really useful. Here are the main topics I am doing about: How strong is the bone? I need to talk about the breaking stress and include some of the young modulus in there too. I need some data about that and possibly compare to other materials. How does a bone break? I need to talk about tension and compression and basically how a bone breaks. What happens to the bone as we get older? I need to talk about how and why the bone gets weaker as we get older. Anything would be useful, especially data and diagrams. It would be a great help and I congratulate you if you read the full post. Thanks...