Need Engineering Help

just looked through my statics book. I agree that tension is the same throughout the cable.

 

Yea. And I believe to get the tension in Newtons you multiply that 60 pounds by .45 to get kilograms. Then multiply that by gravity which is 9.81. So you get a tension in all three cables of 267 Newtons.

 

I was also thinking that too, but he told me it is a real life example, but didn't know what the friction was. So he is looking up the coefficient of friction for the pulley.

 

If you don't know the friction, you can't determine the tension in the cable. There is no friction constant for a pulley

 

I don't think he wants to take in consideration the pulley's friction, in order to calculate the friction in each pulley you would need to know the tension at both side of the pulley which is what are you looking for, for example for the pulley on the left you would need to know the tension of L2 and L3, but the tension if considering friction is unknown at least for L2 in that case. The angle is given (which is related to amount of cable in contact with the pulley) so covert 137.6 degrees to radians and therefore the coefficient of friction for that pulley is u = (1/(Angle in Radians))ln(L2/L3) if I remember correctly...

 

What it is.. he is working alongside a teacher for credit and this is one of the problems he gave him to do. It is from a consulting job the teacher is doing. It uses a boat crank to open a door mounted below. Pretty nutz and I stared at it for a good while and I dont remember going over it either.

 

Then this a far more complex problem, the length of L1 is incorrect from the given information on the diagram, length of L2 is incorrect from the information in the diagram, even the length of L3 is wrong. Look at what is defined as the length of L3 which is given as 54", then look at the measurement in the right side says 38" . 54" is not equal to 38", the rest of the lengths you will see that they are wrong if you use the given information in the diagram and Pythagorean theorem. If this is a real life problem like stated above then there is a lack of information.

 

yea I think thats why they are looking for the tension... I told him 1 crank + 1 big strong worker = enough power... lol

 

Yea he told me that it wasnt drawn to any sort of scale...just rough sketch in either autocad or paint lol

 

If the crank is not moving, then it is a statics problem and there is no friction at all. And even if it is moving, it seems the friction would be practically negligible for the pulleys.