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Phy 121
Your 'cq_1_12.1' report has been received. Scroll down through the document to see any comments I might have inserted, and my final comment at the end.
** CQ_1_12.1_labelMessages **
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Masses of 5 kg and 6 kg are suspended from opposite sides of a light frictionless pulley and are released.
• What will be the net force on the 2-mass system and what will be the magnitude and direction of its acceleration?
answer/question/discussion: ->->->->->->->->->->->-> :
The net force is the mass times acceleration. The net force exerted on the system will be (5kg * 9.8m/s^2) + (6kg * 9.8m/s^2) = 107.8N
The magnitude of the acceleration will be the force exerted on the 6kg mass by gravity divided by the mass.
A = Fnet (6kg*9.8m/s^2 = 58.8 N) / m (6kg) = 9.8m/s^2
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• If you give the system a push so that at the instant of release the 6 kg object is descending at 1.8 meters / second, what will be the speed and direction of motion of the 5 kg mass 1 second later?
answer/question/discussion: ->->->->->->->->->->->-> :
Vo = 1.8m/s
A = 9.8m/s
`dt = 1 s
The product of the acceleration and the change in time is the change in velocity
`dv = 9.8m/s
The sum of the initial velocity and the change in velocity is the final velocity
Fv = 11.6m/s
The average of the initial and final velocities is the average velocity
vAve = 6.7m/s
The product of the average velocity and the time interval is the distance travelled
`ds = 6.7m
We previously identified that the downward descent of the 6 kg object positive as well as the direction of the 5kg object moving up the incline is positive.
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• During the first second, are the velocity and acceleration of the system in the same direction or in opposite directions, and does the system slow down or speed up?
answer/question/discussion: ->->->->->->->->->->->-> :
The velocity and the acceleration are both moving in the same direction provided that the surface on which the 5 kg object is flat with a slope of 0. If the slope increased this would make the velocity of the 5 kg object negative since it would be moving up technically. The acceleration of gravity pulling the 3 kg object down increasing its velocity would both be positive.
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about 30 minutes
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The masses are on opposite sides of the pulley. The force on one side therefore opposes the force on the other. The two forces tend to accelerate the system in opposite directions.
Clearly if you hang two nearly-balanced weights over a pulley, they don't accelerate downward at the rate of a freely falling object.
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Solution
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