Magnetic and Electric Fields problem

AI Thread Summary
In the discussion about magnetic and electric fields, participants explore the relationship between gravitational force and magnetic force acting on a wire. The main focus is on determining the conditions under which a wire carrying a 40 A current can "float" in a magnetic field generated by another wire. To achieve this, the required magnetic field strength (B) is calculated first, followed by the necessary current in the stationary wire to produce that magnetic field at a specific distance. Oersted's law is referenced to explain the principles at play in this scenario. The conversation emphasizes the calculations needed to balance gravitational and magnetic forces for the wire to remain suspended.
davidj
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Homework Statement
A straight wire of linear mass density 150 g/m has a
current of 40.0 A (supplied by a flexible connection of
negligible mass). This wire lies parallel to, and on top
of, another straight horizontal wire on a table. What
current must the bottom wire have in order to repel
and support the top wire at a separation of 4.0 cm
Relevant Equations
fg = mg
fm = qvbsin(theta)
BIL = mg
Would i assume that fg = fm (force gravity holding straight wire down is equal to the magnetic force) and isolate for I?

Help if you're available please!
 
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Are you familiar with Oersted's law?
 
yes i am but how you mind explaining how its applicable in this situation
 
davidj said:
yes i am but how you mind explaining how its applicable in this situation
The wire that is supposed to "float" is subjected to the magnetic field that comes from the wire that is lying on the table.

First, calculate what B is required for the wire with 40 A current to "float". Then you figure out what current is required in the cable lying on the table to produce this magnetic field at the desired distance.
 
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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