Question

@mathmale




If Sheila has to pull 5 m of rope to move an object up to her tree house using a fixed pulley, how much rope will she have to pull if she attaches a moveable pulley to the object?

5 m
2.5 m
10 m
20 m

Answer 1

I think answer will be option D

Answer 2

Because for one pulley,we have to pull double the rope to reach at top height,
so for double pulleys,we have to pull it 4 times

Answer 3

Thank you for explaining your thinking. You may be right. However, I believe there's one fixed pulley above the object being lifted, and one more pulley (which moves up and down as the rope is pulled. Please see the diagram I drew for Noah.

Answer 4

so as per your directions, we have to pull only 10m rope

Answer 5

@mathmale

Answer 6

because one is fixed and other is movable

Answer 7

That's right. 10 feet of rope will lift the object 5 feet up. Good.

http://openstudy.com/study#/updates/5680aae7e4b012befebab3fc

Answer 8

but what is the purpose of that movable pulley ?

Answer 9

for reduce our effort ,right ?

Answer 10

The whole story is about "mechanical advantage. Yes, adding pulleys reduces the amount of pull on the rope necessary to lift the object. The down side is that you have to pull more rope through the upper (fixed) pulley.

Answer 11

Thank you @mathmale for your kind help !

Answer 12

My pleasure. Take care! Bye

Answer 13

you too !