Two Masses Hanging on a Massive Pulley


by Becca93
Tags: masses, massive, pulley
Becca93
Becca93 is offline
#1
Dec4-11, 01:48 PM
P: 84
The problem statement, all variables and given/known data
A pulley with mass Mp and a radius Rp is attached to the ceiling, in a gravity field of 9.81 m/s2 and rotates with no friction about its pivot. Mass M2 is larger than mass m1. The quantities Tn and g are magnitudes.

(image attached)
Select T-True, F-False, G-Greater than, L-Less than, E-Equal to.
A) T1 is ..... m1g.
B) T2 is ..... T1.
C) The magnitude of the acceleration of m1 is ..... that of M2.
D) The center of mass of Mp+M1+M2 accelerates.
E) T1 + T2 is ..... T3.
F) m1g + M2g + Mpg is ..... T3.


The attempt at a solution

A) G - Because the m2 is greater than m1, the system is accelerating left, so tension in string one would be the weight plus ma.
B) L - System is accelerating left over a pulley, so would tension less?
**I'm not sure about this one. Would they be equal?
C) E - The whole system is accelerating, so they should be equal.
D) T - I said true for this one because the distances of m2 and m1 from Mp are constantly changing.
E) L - T1+T2 is responsible for only m1 and m2. T3 is responsible for m1, m2, and Mp, so therefore T1+T2 should be less than T3
F) E - T3 is responsible for the weight of all three masses.
**I'm not sure about this one either. Would moment of inertia or any other rotational force factor in here to make T3 greater?

I've tried GLETLE AND GEETLE and both combinations are incorrect. There is a flaw in my reasoning and I am unable to see where it is.

Any advice?


Edit: My tries are as follows:
1 Incorrect. (Try 1) GLETLE
2 Incorrect. (Try 2) GEETLE
3 Incorrect. (Try 3) GEETLL
4 Incorrect. (Try 4) GLETLL
Attached Thumbnails
prob23_Atwood2.gif  
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grzz
grzz is offline
#2
Dec4-11, 02:15 PM
P: 939
I would think again re

B,D, E ... and I am still thinking re F!
Becca93
Becca93 is offline
#3
Dec4-11, 02:28 PM
P: 84
Quote Quote by grzz View Post
I would think again re

B,D, E ... and I am still thinking re F!
But why? Am I missing a law or something?

grzz
grzz is offline
#4
Dec4-11, 02:30 PM
P: 939

Two Masses Hanging on a Massive Pulley


re B

The pulley needs a torque so that it can rotate. Hence T2 is .... than T1.
grzz
grzz is offline
#5
Dec4-11, 02:36 PM
P: 939
I think your F is ok.
Becca93
Becca93 is offline
#6
Dec4-11, 02:36 PM
P: 84
Quote Quote by grzz View Post
re B

The pulley needs a torque so that it can rotate. Hence T2 is .... than T1.
So T2 is greater than T1?

Okay. So, would
a-G
b-G
c-E
d-T
e-L
f-L

sound right?
grzz
grzz is offline
#7
Dec4-11, 02:47 PM
P: 939
So T2 is greater than T1?....I think yes.

re D

If m2 goes down through distance x , what is the distance gone up by m1?
Becca93
Becca93 is offline
#8
Dec4-11, 02:50 PM
P: 84
Quote Quote by grzz View Post
So T2 is greater than T1?....I think yes.

re D

If m2 goes down through distance x , what is the distance gone up by m1?
The following are my incorrect answers:
1 Incorrect. (Try 1) GLETLE
2 Incorrect. (Try 2) GEETLE
3 Incorrect. (Try 3) GEETLL
4 Incorrect. (Try 4) GLETLL
5 Incorrect. (Try 5) GGLFLL
6 Incorrect. (Try 6) GGEFLL
grzz
grzz is offline
#9
Dec4-11, 02:57 PM
P: 939
If m2 goes down through distance x , what is the distance gone up by m1?
grzz
grzz is offline
#10
Dec4-11, 03:00 PM
P: 939
re E

Is the pulley accelerating downwards or upwards?


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