Two masses connected by a string uniform circular motion. HELP

AI Thread Summary
The problem involves two masses, m1 and m2, connected by a string, where m1 revolves in a circle on a frictionless table while m2 hangs stationary. The tension in the string is crucial for maintaining m1's circular motion, calculated as T = m1v^2/R. The weight of m2, expressed as T = m2g, provides the necessary force to keep m2 in equilibrium. Both expressions for tension must be consistent, reflecting Newton's third law, which states that forces exerted by the string on both masses are equal. Understanding the relationship between the two masses is essential for solving the problem.
MelissaJL
Messages
50
Reaction score
0
Two masses connected by a string uniform circular motion. HELP! :)

Homework Statement


6-p-054.gif

A puck of mass m1 is tied to a string and allowed to revolve in a circle of radius R on a frictionless, horizontal table. The other end of the string passes through a small hole in the center of the table, and an object of mass m2 is tied to it. The suspended object remains in equilibrium while the puck on the tabletop revolves.

What is the tension in the string? (Use any variable or symbol stated above along with the following necessary: g.)

So. I keep looking at this problem...there's more questions to this but the first part is stopping me from completing the others. I was wondering how does the mass m2 effect the tension in the string if it is stationary? I know the tension for mass m1 by itself would simply be T=m1v2/R. Also that if I isolated mass m2 the tension would simply be T=m2g. How do I incorporate them or is one case null? Any suggestions? Thank you :)
 
Physics news on Phys.org


You have it sorted out!
The tension needed to keep m1 in circular motion is m1v^2/R. This is the centripetal force.
This force is provided by the WEIGHT of m2 =m2 x g.
Think of Newton's 3rd law. If the string is pulling on m1 with a force F then the string must be pulling on m2 with a force F. (remember there is no friction to worry about)
 


You got it - both expressions have to be correct.
However, one of them uses a variable or symbol not supplied and you are restricted by the terms of the question to use only those which are supplied.
 
Thread 'Variable mass system : water sprayed into a moving container'
Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
Back
Top