Wire tension and motion in a pulley system

AI Thread Summary
The discussion focuses on calculating the tension in a wire system where Joey and Caitlin hang from opposite ends of a pulley. Joey's mass is 75.0 kg, and Caitlin's weight is 637 N, leading to the need for equations derived from Newton's second law to find the tension. It is established that Caitlin cannot change the system's motion without external forces, as any force she exerts on Joey through the rope results in an equal and opposite reaction, maintaining the system's state. The participants clarify that the internal forces do not affect the overall motion of either person or the rope. The conversation emphasizes the importance of understanding forces and motion in a pulley system.
mezmorize
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Hello everyone, i need help with these 2 question from physics. I am a year 11 physics student.

Joey and Caitlin hang from two ends of a wire, looped through an ideal pulley. Joey has a mass of 75.0Kg, whilst Caitlin weighs 637N.

a) calculate the tension of the wire?

b) If Caitlin is not able to reach out and touch anything, is she able to change the motion of the system? Why?
 
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mezmorize said:
a) calculate the tension of the wire?

What forces act on which of them? In this case, it's easy to determine directions of their motion and calculate acceleration.

mezmorize said:
b) If Caitlin is not able to reach out and touch anything, is she able to change the motion of the system? Why?

Some kind of force is required to change the motion of the system. Now, is there any way to obtain that force if Caitlin can't touch anything (just remember the definition of force)?
 
a) From Newton 2nd law applied to catlin and joey we get the following two equations.
W_C-T=m_Ca_C
W_J-T=m_Ja_J where T is the tension of the wire. All you need to do is solve this system of equations for T, given that a_C=-a_J where minus sign comes from fact that they ll move in opposite direction(if one is going up the other will go down).

b) If caitlin is not able to reach out and touch anything except the rope, then the only force that caitlin can exert is to Joey through the rope. But then due to Newtons 3rd Law, Joey will exert an equal but opposite force to caitlin. Because caitlin and joey are connected with the rope, this internal force cannot change the motion of neither of them, neither the motion of the rope, it just increases the tension of the rope.
 
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N-Gin said:
What forces act on which of them? In this case, it's easy to determine directions of their motion and calculate acceleration.



Some kind of force is required to change the motion of the system. Now, is there any way to obtain that force if Caitlin can't touch anything (just remember the definition of force)?

thanks :), I've calculated the acceleration which is 0.7ms-2 but i can still seem to find out how to find the tension :S
 
ahhhh don't worry delta explained it xD
 

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