Last Question on long Physics HW, please help out!!!?

Question

Im not too good with friction and newtons laws, so i dont know where to start with this. I was able to figure out all but two problems on my HW packet, and i dont have a book so if someone can show me how to do this last problem, i will be very greatful (and can finally get some sleep :)

A 100kg fireman is being lowered from a floor 10 meters above the ground by a rope whose breaking strength is 800 N. The fireman starts from rest and the person lowering the frieman knows the 800 N limit must be adhered.
Draw a free body diagram showing all the forces exerted on the fireman.
What is the fireman velocty when he touches the ground?
The fireman moves 20 cm during his stopping. What is the average normal force exerted on the fireman during the stop?


Thats the question. Since i dont have a book, for the past hour iv been trying to find similar questions and forumlas online to no luck, so i had to resort to asking here. I hope someone here can please help with this question.

Answer 1

the idea is that the fireman is accelerating such that ma=mg-800N, the 800N is exerted by the person holding the fireman and is facing up, the force on fireman that is pointign down is mg (a is his acceleration). where ma is mass of fireman times his acceleration. 1. find a
2 find v, given that d=v^2/(2a) [from: d=at^2/2, v=at] where d is 10m
3. knowing v, the ave force of impact is calculated based on impact energy and dissipation of this energy in frictional force acting for 20cm: mv^2/2=F*d, find F..., where d=20cm

Answer 2

Maximum
Tension on rope=800N
^
1
1
[Fireman] u=0
1
1
v
Weight of fireman=100*g
=980N
v=?

Given: s=10m
u =0


Distance moved after stopping=20cm
=0.20m

Looking at our free body diagram, we see that the weight of the fireman, 100*9.8 (=980N), is bigger than 800N. The rope will break. The fireman will thus fall and accelerate downwards at 9.8m/s^2. His velocity will be given by the formula:

v^2-u^2=2as where v is his velocity at the bottom, u the initial velocity which is 0, a the acceleration of gravity of 9.8m/s^2, and s is the height of 10m. Substitute known values:

v^2- 0=2*9.8*10
=196
v=14m/s.

His Kinetic Energy, KE, at the bottom will be converted to work by the force exerted on him over a distance of 0.20m. Based on the principle of conservation of energy:

KE=Work
1/2mv^2=F*s

m is his mass, v his velocity, F is the force exerted on him, and s is the given distance moved.
Substitute known values:

1/2*100*14^2=F*0.20
9800=F*0.20
F=9800/0.20
=49,000N

Will the fireman survive the fall?

Answer 3

stephen king, eyes of the dragon. read it, if youve got time, love the way he started tieing g>vs its really strange how he tied the alt univers of rolands existence and our present as well as his past and etc, nice way to describe equalization or what happens when + and - matter collide, you get the longoliers neat huh, thanx mr. king and fte to u and yours.

trains are also a neat way to watch breaking strain in action, its used to get em started as well as stopped. between every car is a resistance connection(hitch) that moves in out or in, so it kinda works like a bottleneck. the pre and post jam.

also i forgot the other force exerted, hmmmmm lowering firefighter thinking of lowered firefighter,"i wonder if he'll bounce or just patte`" lets find out lol, human beings are at best a little loki'ish lmao.