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Old Sep 20th 2009, 04:34 PM   #1
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Modified Atwood Machine

I'm really having trouble with these problems.

I'm given a modified (semi) Atwood machine with a mass being "dragged" up an incline of 30 degrees. The mass of the block on the incline is 0.800kg and the mass of the other block is 0.500kg.

I draw the FBD and I come up with a tension force parallel to the incline, a gravitational force pulling downward and the normal force exerted by the incline itself.

I'm not really sure where to go from here, though...
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Old Sep 21st 2009, 05:56 AM   #2
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Let T be the tension in the string. Since 0.8 kg is being dragged up the incline, the 0.5 kg mass is moving down. Hence,

(0.5) g - T = (0.5) a .

Along the incline,

T - (0.8) sin 30 = 0.8 a.

The normal reaction of the block on the incline is not considered here as it does not contribute to the motion along the incline.

If friction were present, this too would need to be considered.

Note that since the string is "incompressible" i.e maintains its length, the distance moved by one mass along the plane is equal to the distance traveled down by the other.

I leave the rest to you.
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Old Sep 22nd 2009, 08:49 AM   #3
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Thank you, I was able to solve this problem.
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