- #1
Dahaka14
- 73
- 0
Okay, I just took a test where there was a loop with a bar and a resistor in a magnetic field going into the screen as follows
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l____(bar)_____lxxx
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where the bar starts at rest, and begins to accelerate vertically down due to gravity. We were asked to find the final velocity (which I understand), and then AFTER IT HAS REACHED TERMINAL VELOCITY find the power dissipated through the resistor as a function of time and the work done by gravity as a function of time.
At first I set P=IR^2, and solved using the terminal velocity I found. But then I thought that the current isn't changing, because the velocity is constant, so I assumed it would be zero. I am very shaky on this one, and it's probably wrong, right?
Then, for the work done by gravity, I set W(t)=mgh=mgvt. But then I remembered the work-energy theorem, and there is no change in kinetic energy due to its constant velocity, and there is no net force on it anyhow. What are the answers?
____/\/\/\_____
lxxxxxxxxxxxxxxxlxxx
lxxxxxxxxxxxxxxxlxxx
lxxxxxxxxxxxxxxxlxxx
lxxxxxxxxxxxxxxxlxxx
l____(bar)_____lxxx
lxxxxxxxxxxxxxxxlxxx
lxxxxxxxxxxxxxxxlxxx
lxxxxxxxxxxxxxxxlxxx
lxxxxxxxxxxxxxxxlxxx
where the bar starts at rest, and begins to accelerate vertically down due to gravity. We were asked to find the final velocity (which I understand), and then AFTER IT HAS REACHED TERMINAL VELOCITY find the power dissipated through the resistor as a function of time and the work done by gravity as a function of time.
At first I set P=IR^2, and solved using the terminal velocity I found. But then I thought that the current isn't changing, because the velocity is constant, so I assumed it would be zero. I am very shaky on this one, and it's probably wrong, right?
Then, for the work done by gravity, I set W(t)=mgh=mgvt. But then I remembered the work-energy theorem, and there is no change in kinetic energy due to its constant velocity, and there is no net force on it anyhow. What are the answers?