Electro-Mechanics with Source

A conducting rod of mass m m slides along a pair of conducting rails which are separated by a distance D D . The rod is pulled rightward by a constant force F F . The circuit is completed by a series combination of a resistor R R , an inductor L L , and an AC voltage source V S V_S . There is an ambient magnetic flux density B B which points into the page.

At time t = 0 t = 0 , the rod has zero speed and there is no current in the circuit. At time t = 5 t = 5 , how far is the rod from its initial position?

Details and Assumptions:
1) m = 1 m = 1
2) D = 2 D = 2
3) F = 2 F = 2
4) R = 2 R = 2
5) L = 1 L = 1
6) B = 5 B = 5
7) V S = 10 sin ( 5 t ) V_S = 10 \sin (5t)
8) There is no gravity
9) Neglect the magnetic field contributions from the rails


The answer is 0.1643.

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1 solution

F u n P r o b l e m \textcolor{#20A900}{Fun Problem}
As always, it is a pleasure to solve your problems. Thank you for another good one.

The basic equations are B v D 10 s i n ( 5 t ) i R L d i d t = 0 \textcolor{blueviolet}{BvD-10sin(5t) -iR-L \frac{di}{dt}=0} F B i D = m d v d t \textcolor{blueviolet}{F-BiD=m \frac{dv}{dt}} After substituting value 10 v 10 s i n ( 5 t ) 2 i i ˙ = 0 10v-10sin(5t) -2i-\dot{i}=0 v ˙ + 10 i = 2 \dot{v}+10i=2 Solving both equations, gives the differential equation in terms of v v 10 v + 0.2 v ˙ + 0.1 v ¨ = 10 s i n ( 5 t ) + 0.4 \textcolor{midnightblue}{10v+0.2\dot{v}+0.1\ddot{v}=10sin(5t) +0.4} Solving this differential equation and using initial conditions v ( 0 ) = 0 \textcolor{#624F41}{v(0) =0} v ˙ ( 0 ) = 2 \textcolor{#624F41}{\dot{v}(0)=2} to find the values of arbitrary constant in the solution of differential equation. And after substituting the value of arbitary constants gives the solution of differential equation as v = 1.31004 s i n ( 5 t ) 0.439757303 e t s i n ( 9.94987 t ) + 0.174672 e t c o s ( 9.94987 t ) 0.174672 c o s ( 5 t ) + 0.04 \Large \textcolor{forestgreen}{v=1.31004sin(5t) -0. 439757303e^{-t}sin(9.94987t) +0.174672e^{-t}cos(9.94987t) -0.174672cos(5t) +0.04} Substituting v = d x d t \large v=\frac{dx}{dt} d x d t = 1.31004 s i n ( 5 t ) 0.439757303 e t s i n ( 9.94987 t ) + 0.174672 e t c o s ( 9.94987 t ) 0.174672 c o s ( 5 t ) + 0.04 \Large \textcolor{#BA33D6}{\frac{dx}{dt}=1.31004sin(5t) -0. 439757303e^{-t}sin(9.94987t) +0.174672e^{-t}cos(9.94987t) -0.174672cos(5t) +0.04} x ( 0 ) x ( 5 ) d x = t = 0 t = 5 ( 1.31004 s i n ( 5 t ) 0.439757303 e t s i n ( 9.94987 t ) + 0.174672 e t c o s ( 9.94987 t ) 0.174672 c o s ( 5 t ) + 0.04 ) d t \Large \int_{x(0) }^{x(5)} dx=\int_{t=0}^{t=5}(1.31004sin(5t) -0. 439757303e^{-t}sin(9.94987t) +0.174672e^{-t}cos(9.94987t) -0.174672cos(5t) +0.04)dt x ( 5 ) = 0.165087 \large \textcolor{#3D99F6}{\boxed{x(5) =0.165087}}

Nice job. You're getting good at these

Steven Chase - 1 year ago

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@Steven Chase are you posting one more question today??

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