Solving Variable Resistance Circuit: Ohm's Law

AI Thread Summary
The discussion centers on a circuit with a variable resistance of 100 ohms and a voltage drop of 12 V. Participants are trying to apply Ohm's Law (V=IR) to determine the necessary resistance for two voltage scenarios: 12V and 6.2V. There is uncertainty about whether the problem involves solving for two unknowns and if a diagram is needed for clarity. One participant calculates the current as 8.5 amps for the 12V scenario but expresses doubt about the accuracy of their answer. The conversation highlights the need for clearer problem parameters and potentially a visual representation to aid understanding.
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Homework Statement


"A circuit has a variable resistance (total 100 ohms) across which is a voltage drop of 12 V supplied by a battery. What must be its resistance if the voltage is to be A) 12V and B) 6.2V?"

Homework Equations


V=IR


The Attempt at a Solution


We haven't learned anything besides Ohm's Law for these equations, so I tried plugging in different values to try and dial in the answers, but it didn't work. Is there something I'm missing or am I being asked to solve for two unknowns? Hints appreciated.
 
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Is that all you have? Diagram? I am assuming total resistance is 100 ohms so for 12 v you have 8.5 amps. Then for 12V, you need a resistance of 12/8.5 but I don't trust this answer. If its a serial pair of resistors where Rx and Ry are 100 ohms and you are being asked the voltage drop across Rx, i think the above is good.
 
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drawing a blank on the diagram, literally
 
Thread 'Variable mass system : water sprayed into a moving container'

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}...
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