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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?
9.8 m/s^2 * 5 kg = 49 N
9.8 m/s^2 * 6 kg = 58.8 N
Fnet = 58.8N – 49N = 9.8 N
Magnitude is the 5 kg and 6 kg masses = 11 kg
Direction of acceleration is positive in the upward direction of the 5 kg mass as the 6 kg mass moves it upward. A = 9.8 N/ 11 kg = .891 m/s^2
• 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?
Vf= v0 + a`dt^2
Vf= 1.8 m/s + .891 m/s^2 (1s)^2
Vf = 2.691 m/s
The speed will be 2.691m/s at 1 second later. The direction of motion will be downward since there was an initial push. This would make the motion to be going in the negative direction.
The system accelerates in the direction of the 6 kg object, so if it's moving in the direction of the 5 kg object it will be slowing.
The system can move in one of two directions, one in which the greater mass is descending, one in which the lesser mass is descending. You have to pick one of these directions as your positive direction. Do so. It doesn't matter which one you pick, but once you make the choice, you need to stick with it.
Relative to your chosen direction, is the given velocity positive or negative? Is the acceleration positive or negative?
What therefore are the initial velocity, acceleration and time interval?
You can reason out all the other quantities from these.
• 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?
During the 1st second, the velocity and acceleration are going in opposite directions. They are going in opposite directions because the velocity is going in the positive direction but because of the push, the acceleration is going in the negative direction. During the 1st second the system slows down from the initial push because gravity takes over in this second and the 6 kg mass begins to pull the 5 kg mass upward.
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20 min
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I'm not sure about the magnitude. I'm eager for your explanation.
You're on the right track.
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