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Waiting for the TE. Need one answer from CP, ferris wheel edition. Maybe a physics person can help too.


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I accidentally bought the wrong teacher's book and so have been trying to learn Physic's along side my son. I'm going to cave and buy the proper TE shortly. We're stuck on chapter 5 question 44.

Here's the questions:

 

43. A 10kig mass on a horizontal friction-free air track is accelerated by a string attached to another 10kg mass hanging vertically from a pulley. What is the force due to gravity in newtons of the hanging 10 kg mass? What is the acceleration of the system of both masses?

 

44. Suppose the masses described in the preceding problem are 1 kg and 100 kg, respectively. Compare the accelerations when they are interchanged, that is, for the case where the 1 kg mass dangles over the pulley, and then for the case where the 100 kg mass dangles over the pulley. What does this indicate about the maximum acceleration of such a system.

 

I'm assuming the pulley is friction free too. I just can't seem to wrap my mind around this one. Either the mass on the table will affect the system or it won't. Intuitively, I think that it should but then I'm used to friction. If I take the pulley out of the system and make the whole system vertical then the weights don't matter. Acceleration will be g.

 

Can anyone explain this to me? If you just have the TE even just the answer would be helpful.

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I accidentally bought the wrong teacher's book and so have been trying to learn Physic's along side my son. I'm going to cave and buy the proper TE shortly. We're stuck on chapter 5 question 44.

Here's the questions:

 

43. A 10kig mass on a horizontal friction-free air track is accelerated by a string attached to another 10kg mass hanging vertically from a pulley. What is the force due to gravity in newtons of the hanging 10 kg mass? What is the acceleration of the system of both masses?

 

44. Suppose the masses described in the preceding problem are 1 kg and 100 kg, respectively. Compare the accelerations when they are interchanged, that is, for the case where the 1 kg mass dangles over the pulley, and then for the case where the 100 kg mass dangles over the pulley. What does this indicate about the maximum acceleration of such a system.

 

I'm assuming the pulley is friction free too. I just can't seem to wrap my mind around this one. Either the mass on the table will affect the system or it won't. Intuitively, I think that it should but then I'm used to friction. If I take the pulley out of the system and make the whole system vertical then the weights don't matter. Acceleration will be g.

 

 

43. 

Assume pulley is frictionless and massless and string is massless and unstretchable.

The weight of the hanging mass has to provide the acceleration for the entire system

The force is mg=98 N. The acceleration it provides to the entire system can be found from Newton's 2nd Law : F=Ma where the total mass has to be 2*m with m=10kg.

mg=2ma

a=g/2.

Edited by regentrude
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44: The weight of the hanging mass has to provide the acceleration of the entire system.

If we call the masses m1 (hanging) and m2 (surface):

F=Ma

m1*g=(m1+m2)*a

 

a= m1*g/(m1+m2)

 

If m1 <<m2, the acceleration is very small.

If m1>>m2, the acceleration approaches g, but cannot ever exceed g.

 

 

Edited by regentrude
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Thank you. I'm so rusty. It's been nearly 20 years since I did physics and my brain is mush from the constant distractions from all my littles. If he wants to go past this book I'm going to have outsource. Maybe these efforts will help prevent Alzheimer's disease.

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