Question

A large engine with mass of 400 kg must be lifted 3 meters out of a truck for repair. A normal mechanic can lift with about 250 N of pulling force. They use a system of pulleys to do this. If we assume the engine starts on the ground, how long must the ropes be on the pulley to allow the mechanic to lift this engine that distance?

(hmmm... I am really not sure how to go about this problem... Can anyone help give me some ideas? Thanks!)

Answer 1

400*9.81 = 3924 Newton weight

I guess the mechanic is also on the ground?mechanical advantage needed = 3924/250 = 15.7
since pulleys do not come in fractions we will need 16 times
16*3 = 48 meters

Answer 2

You will need a MA of 2, so the rope must be twice as long as the hehttps://www.easycalculation.com/engineering/mechanical/simple-machines/mechanical-advantage-pulley.phpight raised.

Answer 3

Thanks everyone! I think those answers make sense. I ended up doing something a little different though.

First I found the velocity using 1/2mv^2i+mghi=1/2mv^2f+mghf
and got v=7.7m/s

Then I plugged that into W=change in KE
or 1/2mv^2f-1/2mv^2i = Fd
and got d=47.432m

close to Damon's answer! :D

Answer 4

Well, yes but it was the change in POTENTIAL energy m g h. The velocity is assumed negligible.

Answer 5

Oh but does the way that I did it count too? I think I might still be quite confused.

Answer 6

halp