Force -displacement graph question

[Lolagoeslala]

Homework Statement

A crate, having a mass of 45 kg is pulled steadily upwards by tw ropes through a height of 12 m. Each rope has mass of 0.75 kg/m. Draw the F-d graph and determine the work done in pulling the crate 12 m.

The Attempt at a Solution

Alright...

so we know that we are starting with
m1 = 45 kg
m2 = 0.75kg/m x 12 m
m2 = 9 kg x2
m2 = 18 kg

Now we need to find the force that it will have initially ...

Fn = mg
Fn = (18 kg + 45 kg)(9.8m/s^2)
Fn = 617.4 N

Now after the crate has been pulled 12 m ...
it'll only have m1 attached which is 45 kg

Fn=mg
Fn=(45kg)(9.8m/s^2)
Fn=441 N

Now i made this graph...

http://s1176.beta.photobucket.com/user/LolaGoesLala/media/ih.jpg.html

Then i used this formula..

W = (A+B/2)(d)
W = (617.4 N+ 441 N/2)(12 m)
W =6350.4 J

 

[Simon Bridge]

OK that's great - did you have a question?