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  1. sojsail

    Gravitation (planetary motion)

    Is it possible that your sketch is a misinterpretation of the problem description? If p is on the orbit, when the particle comes around to the location of p, the force would become infinite (with n being a negative exponent). I am assuming that r is the distance to p. And in that case, I can not...
  2. sojsail

    Acceleration graph

    In graphs of a thrown ball, assume that time starts when the ball leaves the hand. So would the acceleration of the throwing motion be part of the graph?
  3. sojsail

    Acceleration graph

    If you are confused by what is said in any of our posts, likely any of us that are connected could explain/reword the post for you. We don't explain how to get the answer, but if necessary we can explain posts that have come in for you.
  4. sojsail

    Newton's Second Law — Net Force problem

    I think your solution is equivalent to one of a list of perhaps 2 or 3 methods that would get full credit. One quibble about your worksheet: in one line you gave g as the unit where I think you knew, from how you converted the numerical part, is kg. That could cost you. There were several...
  5. sojsail

    Velocity-time graph

    Could it be that you intended to ask about acceleration?
  6. sojsail

    Why can we ignore certain circuit paths?

    I found this to be an interesting discussion. I can not tell if the worry has been eliminated, so I would like to add my way of seeing that. Current would be flowing down the schematic thru R1. Let the potential of the "horizontal wire" be Vh. What if some current tried to continue going down...
  7. sojsail

    Forces and vectors: pulling a baby buggy on soft ground

    Where did the 64 come from? Certainly not the 64 N in frame #8. In which direction are you now trying to work out the total force -- total force exerted on the ground?
  8. sojsail

    Kirchhoff's law problem with two batteries

    Another approach: You know that the ammeter reading is to be zero. So assume that is the case and simplify your equations accordingly.
  9. sojsail

    How is the moment at A using the Force 1200N calculated?

    You are asked to find moment of this Force about point A. Don't assume the bracket is going to rotate to a new position. This would be an analysis of the twisting torque on the bracket (perhaps to see how strong the bracket needs to be considering what will be applied to it in use). Doc Al said...
  10. sojsail

    Time it takes to swim across a river

    I am back. I see that Orodruin caught me misreading the problem. He swims at 4 kph, so the minimum time to the opposite shore would be 540 s. So the book's 624.3 s may be right Edit: since the landing point is to be exactly opposite. Picture yourself at the bank of the river about to jump in...
  11. sojsail

    Time it takes to swim across a river

    I need to sign off for tonight. I hope someone else will take up monitoring and aiding your progress.
  12. sojsail

    Time it takes to swim across a river

    Doc Al said Doc Al's "at an angle" means not perpendicular. Your vertical and horizontal sides would be perpendicular, would they not?
  13. sojsail

    Time it takes to swim across a river

    OK, please describe your triangle.
  14. sojsail

    Time it takes to swim across a river

    Here is a nudge: Review Doc Al's post #8.
  15. sojsail

    Time it takes to swim across a river

    Yes, there is an error somewhere. Before we knew that the goal was to go straight across the river, I worked it out assuming all of his speed would be dedicated to getting across the river quickly. That would yield the minimum time considering his speed and width of the river. That time was 1080...
  16. sojsail

    Time it takes to swim across a river

    OK, please let us know if Doc Al's last post has helped you see how to make progress on this.
  17. sojsail

    Time it takes to swim across a river

    To clarify: when you say upwards, do you mean what I would call upstream (edit: or upriver)?
  18. sojsail

    Falling Chicken

    I recommend the advice in post #2. So that means to develop an expression for delta T in terms of m, g, h, and c.
  19. sojsail

    Finding the depression and the tension of the string

    Please explain your equation: You said in your original post that x is the hypotenuse. Perhaps you should draw the triangle of which x is the hypotenuse. Then explain what is lo, Δl, and y. Perhaps just draw it for yourself (if posting a photo would be a problem) and see if you do not see an...
  20. sojsail

    Sliding on a water slide

    Perhaps it should have said ?? That would mean the hypotenuse is sqrt(5^2 + 25^2) m.
  21. sojsail

    Voltmeter problem from (OCR paper) multiple choice

    Yes, the procedures done to go between the 2 views in the 2 cases are equivalent. In the first, the external resistor is added by throwing the switch, in the second, the external resistor is added by getting out the soldering iron (or similar method of connection).
  22. sojsail

    What are the names of these "F" arrows in these three diagrams?

    Another way to tell you verbally how to draw the resultant of Fx and Fy (top left fig): Imagine Fx and Fy being 2 sides of a rectangle. Now add the other 2 sides of the rectangle (each equal length and parallel to Fx and Fy). Now draw a vector that is a diagonal of the rectangle starting from...
  23. sojsail

    Circuit Analysis Question -- Solving for a multi-resistor circuit

    Your book's answers are wrong on this question!!! Your last post showed significant confusion caused by the error in your book saying what the answers to these 2 parts should be. I will show you how close you were and hopefully eliminate some confusion. In your initial post, you said . You...
  24. sojsail

    Hard time with this Vector Velocity Problem

    Another way to describe what needs to be done: The plane needs a heading such that its East-West component of its 200 km/hr cancels the wind's 85 km/hr.
  25. sojsail

    What forces affect an astronaut?

    a) In the frame of reference of the station -- which is in orbit around the Earth, if the astronaut is hovering in the middle of a cabin without hitting anything, how is that happening? b) From the point of view of a person on earth, the astronaut circles the Earth several times a day. How is...
  26. sojsail

    Circuit Analysis Question -- Solving for a multi-resistor circuit

    The answer in your book and the statement of the problem that you posted are not compatible. To be sure that you know how to solve those questions, please answer this: Just from the statement of the problem, what would your answers be?
  27. sojsail

    Circuit Analysis Question -- Solving for a multi-resistor circuit

    I should make certain that you know - that is the sum R1+R2. So what are the R1 and R2 values? About part b, do you have an answer? Since you understood that 3.75 ohms = 15v/4 amp, I expect that you can find an answer for the current thru R3+R4. Or does does the fact that R3 and R4 have...
  28. sojsail

    Circuit Analysis Question -- Solving for a multi-resistor circuit

    You said "I got 3.75 ohms (15v/4 amp)". I agree with you. There may be an error in the write-up of the problem or in what your book said the right answer should be. For (b), can you explain what the (11.9) means? That might be a clue. Can you ignore a for now and answer b?
  29. sojsail

    Electricity in transmission lines (Simple V^2/R =P)

    I was trying to steer you to a method of solving that I thought would demonstrate a more clear way to look at it: You could calculate the current using P = V*I. And then find the resistance, using as data the above current and the power that is lost to heat (P_lost=1% of P) while that current...
  30. sojsail

    Electricity in transmission lines (Simple V^2/R =P)

    The power lost via P = I^2*R heating is just 1% of the total power. Now, if you only knew the current ...
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