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course Phy 121
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:
5kg *-9.8m/s/s
6kg * 9.8m.s.s
Fnet = -49N +58.8N = 9.8N
9.8N = 11kg * a
A = .89m/s/s
The acceleration will be in the direction of the heavier side (6kg).
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• If you give the system a push so that at the instant of release the 5 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:
5kg * 9.8m/s/s = 49N
6kg *9.8m/s/s = -58.8
V0 = 1.8m/s
T = 1s
Fnet = 49N - 58.8N = -9.8N
-9.8N / 11kg = a = -.89m/s/s
-.89m/s/s = vf - 1.8m/s / 1s
Vf = .91m/s
vAve = .91m/s - .89m/s / 2 = .01m/s = speed
This speed will be in the direction of the heavier wait, so in this case, 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 acceleration are in opposite directions. The system slows down, reaches zero, then speeds up again in the opposite direction.
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