Max Mass Dresser Liftable w/ 150N Force - 46kg

[gmichel395]

Homework Statement

"Using the pulley system shown to lift the heavy dresser, the person is applying a force of 150N to the end of the rope. Which of the following is closest to the maximum mass of the dresser that can be lifted with this force? [Ignore weight & friction from pulleys/rope.]"

A) 46kg
B) 92kg
C) 110kg
D) 150kg
E) 180kg

2. Homework Equations
Newton's 2nd & 3rd laws

The Attempt at a Solution

So she's pulling with 150 N and there are three pulleys connected to the dresser, so her effort is tripled. 450N lifts the dresser and so the mass is 46kg?

 

[gneill]

Label each section of the rope with its tension. How many sections of rope are supporting the dresser?

 

[gmichel395]

I count six sections plus the one the girl is holding so seven. 7*150 divided by g gives approximately 110kg?

 

[gneill]

I count six sections plus the one the girl is holding so seven. 7*150 divided by g gives approximately 110kg?

The one the girl is holding is holding the girl...not the dresser. So one less. You want to count only the ropes that are directly supporting the load.

 

[gmichel395]

Ah so six. And the answer is 92kg?

 

[gneill]

Ah so six. And the answer is 92kg?

Yes.