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what direction does current and electrons flow. can someone please explain what the convention and all means? actual vs conventional?
electron flow vs current flow
- Thread starter Pediateix
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what does it mean electrons will flow from negative to positive, i thouthg this was oppose in electrolytic cells?
Current is conventionally thought of as consisting of positive ions. This was before they figured out that the carrier of charge is the electron. Either way works - one is just right and the other is in widespread use because it's always been used (hence "convention"). When physicists talk about "current," they're talking about the flow of imagined positive charge. But it's implicit that the actual charge carrier is the electron and so electrons flow opposite to the direction of the current. Nobody bothered to change everything because the math works out either way as long as you stick to the convention.
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@Next Step Tutor @NextStepTutor_1
can you please explain questions 1-5, form next step #5-section 1. I really don't understand these questions especially
If the majority of the baseball’s kinetic energy comes from power generation in the legs and hips, approximately how much energy do the lower extremities produce in the pitch?
While evaluating the timing of pitches, the researchers noticed a couple of high-performing athletes who were able to generate higher velocities by increasing the length of their acceleration phase. How did the power production for these athletes compare to those originally mentioned?
can you please explain questions 1-5, form next step #5-section 1. I really don't understand these questions especially
If the majority of the baseball’s kinetic energy comes from power generation in the legs and hips, approximately how much energy do the lower extremities produce in the pitch?
While evaluating the timing of pitches, the researchers noticed a couple of high-performing athletes who were able to generate higher velocities by increasing the length of their acceleration phase. How did the power production for these athletes compare to those originally mentioned?
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Hi Pediateix,
It is definitely a tough passage, but it illustrates how important it is to carefully apply passage information. Here's the basic idea behind all of the questions:
Q1: This basically has two steps: (1) figure out how long the ball is in flight; (2) use that information to calculate how far the ball will fall due to the force of gravity. Once you have that information, you can directly apply it to the scenario in the Q stem (which asks about how high up the catcher's mitt needs to be, not how far the ball fell) to get the right answer.
Q2: Uncoupling the energy chain = less efficient energy transfer to the ball = lower velocity.
Q3: The underlying idea here is that energy transfer to the ball is not perfectly efficient, so the energy generated in the hips must be greater than the energy ultimately imparted to the ball. You can calculate the energy of the ball in the form of its KE, and then use Table 1 to work backwards to calculate the energy that must have been generated in the legs and hips.
Q4: You're asked about power in this question (P = W/t). We're told directly that the t term increases, and can infer that the W term increased too (b/c of the ball having greater KE). This doesn't allow us to conclude anything about the power, or the ratio of W to t. To see this clearly, let's use simple numbers. In scenario 1, 100 J of energy is imparted in 2 seconds. The power is (100 J/2 s) = 50 W. In scenarios 2, 3, and 4, W and t will both increase (like in the Q stem) -- in scenario 2 to 300 J and 3 s, in scenario 3 to 300 J and 6 s, and in scenario 4 to 400 J and 10 s. This will result in power values of 100 W, 50 W, and 40 W, respectively -- so increasing both W and t can lead to greater power, equal power, or less power. We just can't say unless we have specific information. D is the only answer choice that allows us to hedge.
Q5: This is a tough question to visualize, but the key is to recognize that the velocity measurement is made as the ball crosses home plate. At this point, in reality, it will have slowed down. Let's say that the actual initial velocity is 40 m/s and that it slows down to 35 m/s when it crosses home plate. This means that the apparent velocity will be 35 m/s. If the researchers account for air resistance, they will realize that the apparent velocity is lower than the actual initial velocity, and will be able to work backwards to calculate the actual initial velocity. If they neglect it, they'll just say "whatever, close enough, let's say that the actual velocity is 35 m/s". A smaller initial velocity would mean that less energy was transferred to the ball, which would mean that the energy transfer was less efficient.
Hope this helps, and best of luck!
It is definitely a tough passage, but it illustrates how important it is to carefully apply passage information. Here's the basic idea behind all of the questions:
Q1: This basically has two steps: (1) figure out how long the ball is in flight; (2) use that information to calculate how far the ball will fall due to the force of gravity. Once you have that information, you can directly apply it to the scenario in the Q stem (which asks about how high up the catcher's mitt needs to be, not how far the ball fell) to get the right answer.
Q2: Uncoupling the energy chain = less efficient energy transfer to the ball = lower velocity.
Q3: The underlying idea here is that energy transfer to the ball is not perfectly efficient, so the energy generated in the hips must be greater than the energy ultimately imparted to the ball. You can calculate the energy of the ball in the form of its KE, and then use Table 1 to work backwards to calculate the energy that must have been generated in the legs and hips.
Q4: You're asked about power in this question (P = W/t). We're told directly that the t term increases, and can infer that the W term increased too (b/c of the ball having greater KE). This doesn't allow us to conclude anything about the power, or the ratio of W to t. To see this clearly, let's use simple numbers. In scenario 1, 100 J of energy is imparted in 2 seconds. The power is (100 J/2 s) = 50 W. In scenarios 2, 3, and 4, W and t will both increase (like in the Q stem) -- in scenario 2 to 300 J and 3 s, in scenario 3 to 300 J and 6 s, and in scenario 4 to 400 J and 10 s. This will result in power values of 100 W, 50 W, and 40 W, respectively -- so increasing both W and t can lead to greater power, equal power, or less power. We just can't say unless we have specific information. D is the only answer choice that allows us to hedge.
Q5: This is a tough question to visualize, but the key is to recognize that the velocity measurement is made as the ball crosses home plate. At this point, in reality, it will have slowed down. Let's say that the actual initial velocity is 40 m/s and that it slows down to 35 m/s when it crosses home plate. This means that the apparent velocity will be 35 m/s. If the researchers account for air resistance, they will realize that the apparent velocity is lower than the actual initial velocity, and will be able to work backwards to calculate the actual initial velocity. If they neglect it, they'll just say "whatever, close enough, let's say that the actual velocity is 35 m/s". A smaller initial velocity would mean that less energy was transferred to the ball, which would mean that the energy transfer was less efficient.
Hope this helps, and best of luck!
