Simple Machines B/Compound Machines C

[mjcox2000]

I was intending for one of the two of you to post a question, but I can do another one if you'd like - what would you prefer?

[UTF-8 U+6211 U+662F]

I was intending for one of the two of you to post a question, but I can do another one if you'd like - what would you prefer?

I'm a little bit, err.... preoccupied (code phrase for "I'm on vacation"). Why don't you post a question?

[Unome]

Ok then:

If M2 has a mass of 20.0 kg, and for all pulleys the mass is 1.00 kg and the efficiency is 90.0%, solve for the mass of M1 needed to balance the system (with proper significant figures) (assume all ropes are exactly vertical; I'm not sure how them being at angles would affect the system).

[UTF-8 U+6211 U+662F]

Ok then:

If M2 has a mass of 20.0 kg, and for all pulleys the mass is 1.00 kg and the efficiency is 90.0%, solve for the mass of M1 needed to balance the system (with proper significant figures) (assume all ropes are exactly vertical; I'm not sure how them being at angles would affect the system).

So, I'm guessing I have to use gravity:

Without gravity (Click to Show Hidden Text)

IMA = 2*1*2*1*1 = 4 20.0/4.00=5.00 5.00*0.90=[b]4.5 kg[/b]

I don't remember how to calculate with gravity. Oh well.

[Unome]

Ok then:

If M2 has a mass of 20.0 kg, and for all pulleys the mass is 1.00 kg and the efficiency is 90.0%, solve for the mass of M1 needed to balance the system (with proper significant figures) (assume all ropes are exactly vertical; I'm not sure how them being at angles would affect the system).

So, I'm guessing I have to use gravity:

Without gravity (Click to Show Hidden Text)

IMA = 2*1*2*1*1 = 4 20.0/4.00=5.00 5.00*0.90=[b]4.5 kg[/b]

I don't remember how to calculate with gravity. Oh well.

Incorrect; You don't need gravity to do this.

[UTF-8 U+6211 U+662F]

Ok then:

If M2 has a mass of 20.0 kg, and for all pulleys the mass is 1.00 kg and the efficiency is 90.0%, solve for the mass of M1 needed to balance the system (with proper significant figures) (assume all ropes are exactly vertical; I'm not sure how them being at angles would affect the system).

So, I'm guessing I have to use gravity:

Without gravity (Click to Show Hidden Text)

IMA = 2*1*2*1*1 = 4 20.0/4.00=5.00 5.00*0.90=[b]4.5 kg[/b]

I don't remember how to calculate with gravity. Oh well.

Incorrect; You don't need gravity to do this.

Let's try this (Click to Show Hidden Text)

20.0+1.00=21 21/2=10.5 10.5*2=21.0 21.0/0.90=[b]23.3 kg[/b]

Probably not right... I can't figure out the MA for the second pulley from the rigt.

[Unome]

So, I'm guessing I have to use gravity:

Without gravity (Click to Show Hidden Text)

IMA = 2*1*2*1*1 = 4 20.0/4.00=5.00 5.00*0.90=[b]4.5 kg[/b]

I don't remember how to calculate with gravity. Oh well.

Incorrect; You don't need gravity to do this.

Let's try this (Click to Show Hidden Text)

20.0+1.00=21 21/2=10.5 10.5*2=21.0 21.0/0.90=[b]23.3 kg[/b]

Probably not right... I can't figure out the MA for the second pulley from the right.

Nope. Try doing it backwards or upside down; it helps to have a comparison. Also, every pulley has a separate efficiency of 90%, so they have to be calculated one by one. Thinking about how efficiency actually functions would also help.

[UTF-8 U+6211 U+662F]

This is tough (Click to Show Hidden Text)

20/2=10 10/0.9=100/9 (100/9)/0.9=1000/81 (1000/81)/0.9=10000/729 10000/729*2=20000/729 (20000/729)/0.9=200000/6561=[b]30.5 kg[/b]

[Unome]

Unless I'm doing it wrong (and I don't think I am) no. I think you're messing up somewhere in the beginning.

[UTF-8 U+6211 U+662F]

Unless I'm doing it wrong (and I don't think I am) no. I think you're messing up somewhere in the beginning.

Are the masses of the pulleys relevant?

Answer (Click to Show Hidden Text)

7.62 kg? I'm honestly thinking of just giving up and posting another question.