Force: two pulley problem with 3 masses


by runphysicsrun
Tags: force, pulleys
runphysicsrun
runphysicsrun is offline
#1
Sep25-11, 12:24 PM
P: 10
1. The problem statement, all variables and given/known data
A 0.840- kg glider on a level air track is joined by strings to two hanging masses. As seen in the figure, the mass on the left is 4.85 kg and the one on the right is 3.62 kg The strings have negligible mass and pass over light, frictionless pulleys. Find the acceleration of the masses and T1 and T2.

Problem and figure


2. Relevant equations

I assume all a's are equal because a of each object has to be equal to the a of the glider.

[itex]\Sigma[/itex]F =ma

3. The attempt at a solution
[itex]\Sigma[/itex]Fobject1=T1-W
m*-a=T1-(4.85*9.81)
T1= -4.85a+4.85*9.81 (equation 1)


[itex]\Sigma[/itex]Fobject2=T2-W
3.62a=T2-(3.62*9.81)
T2=3.62a+(3.62*9.81) (equation 2)


[itex]\Sigma[/itex]Fobject3=T2-T1
-0.840a=T2-T1 (equation 3)

plugging eq1 and 2 into eq 3
-0.840a=3.62a+35.51-(-4.85a+47.58)
-0.84a-3.62a-4.85a=-12.07
a=.771m/są2
T2=38.3N, T1=38.9N

the answers are a=1.30m/są2 T1=41.3N T2=40.2

I can't figure out what I did wrong!
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Ignea_unda
Ignea_unda is offline
#2
Sep25-11, 12:58 PM
P: 134
Check the file you uploaded - Doesn't look like a physics problem to me.
runphysicsrun
runphysicsrun is offline
#3
Sep25-11, 04:37 PM
P: 10
sorry! -__- the right problem is written in now.


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