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  1. M

    Why do attractive force have a negative sign? like F= -GMm/r^2

    So if there is any difference will the object stay in the orbit or fall down?
  2. M

    Why do attractive force have a negative sign? like F= -GMm/r^2

    kk got it thanks. Hey can I ask you guys another question? What exactly is the difference between centripetal force and gravitational force?? Are they the same? WHY IS acceleration (of free fall) the (resultant) force of the difference between gravitational and centripetal force??
  3. M

    Why do attractive force have a negative sign? like F= -GMm/r^2

    Why do attractive force have a negative sign? The book says its because one must be moving toward the other. But how does it make it negative? I dont understand. Can anyone explain the law of gravitation formula?? F= -GMm/r^2
  4. M

    Finding the escape speed in MArs. Problem on advanced gravitational potential energy.

    Yes yes, that substitution escaped me......I did it that way now. But i am not getting the same answer as i did in the mgh way...any suggestions on why?
  5. M

    Finding the escape speed in MArs. Problem on advanced gravitational potential energy.

    I also know mar's gravitational acceleration. But like i said using GMm/r cannot yield anything because like you know, the masses are in ratio. So I dont know the mass! How can I proceed then??
  6. M

    Finding the escape speed in MArs. Problem on advanced gravitational potential energy.

    Are you sure your method will works? u say ΔKE+ΔPE=0 where ΔPE=(GMm/R).(R/R). But you can't use the formula ΔPE=(GMm/R).(R/R) in this way, you don't know the mass of mars!
  7. M

    Finding the escape speed in MArs. Problem on advanced gravitational potential energy.

    How is the final velocity 0? ANd uve written at the beginning "For excape, r=∞', why do we take that assumption?
  8. M

    Finding the escape speed in MArs. Problem on advanced gravitational potential energy.

    I have no idea what you did after your integration. Can u explain?
  9. M

    Finding the escape speed in MArs. Problem on advanced gravitational potential energy.

    Homework Statement The mean diameters of Mars and Earth are 6.9 10^3 km and 1.3 10^4 km, respectively.? The mass of Mars is 0.11 times Earth's mass. (a) What is the ratio of the mean density of Mars to that of Earth? (b) What is the value of the gravitational acceleration on Mars...
  10. M

    Doubt in resolving forces of a man in an elevator(normal force and weight)

    he full acceleration due to gravity with its appropriate sign would be -g. So why are we not using the this? If it were then we would get (-W), and if we plug this value into the equation N-W= ma we would get N-(-W)=ma which would become N+W=ma. My method is to first find why the elevator is...
  11. M

    Doubt in resolving forces of a man in an elevator(normal force and weight)

    You are saying W=(-9.81m). Right? So now If i plug it into the equatio of N-W=ma won't I end up with N+W=ma ?? And maybe I know this already, but what exactly is the force law?
  12. M

    Doubt in resolving forces of a man in an elevator(normal force and weight)

    (FYI: g does not have a minus sign!) Why not?? It should, considering gravity is acting downwards!!
  13. M

    Doubt in resolving forces of a man in an elevator(normal force and weight)

    it is -(m x -g) which will become +mg
  14. M

    Doubt in resolving forces of a man in an elevator(normal force and weight)

    (Before I start, due to the use of vectors let me state I consider up to be positive and down to be negative) Imagine a scenario, of a man in an elevator. And the elevator is accelerating upwards. Now in this case the Normal force > weight. So Normal Force - Weight =mass X acceleration. If...
  15. M

    A thought question on circular motion, of a car travelling in flat road vs banked rod

    Well its just a rough variable, think of you driving in a constant circular motion. Once in a flat road and then in a banked road. If you were to keep all variables the same, velocity, road surface, tyre grip etc which terrain would you find easier to maintain the circular motion?
  16. M

    A thought question on circular motion, of a car travelling in flat road vs banked rod

    Yes, this is the type of answers, Im loooking for. Theyre easy to understand, and is in the same line of my thinking! But i have a question 'because there is a component of your weight that is parallel to the incline, that helps you out.' How exactly does Mg(weight) have a component parallel...
  17. M

    Centripetal force confusion

    Yes, thats exactly my point! How? If i take one instant, of the car in the circular motion, the velocity will be acting at a tangent. This is because the force of the engine, is acting straight(i.e at a tangent to the circle), and hence shouldn't friction oppose this motion, acting at the...
  18. M

    A thought question on circular motion, of a car travelling in flat road vs banked rod

    I was wondering, if I were to drive in a flat road , and then on a banked road(steep), in a circular motion, which one would be more difficult to manoeuvre over. I thought of generalising the two, but obviously it won't work because in the flat road, it is the frictional force that acts as the...
  19. M

    Centripetal force confusion

    I am probably reviving a dead thread, but am not a troll. I wanted to ask, since the topic is already present, how exactly does the frictional force(which is acting as the tangent to circle tight?) act as a centripetal force. Can some one show it by a diagram or something?
  20. M

    In a clock why does the tip of the hand move faster than somewhere near the centre?

    okay Imagine a car turning in a levelled road. The vertical forces are balance, s there is no vertical acceleration. In the horizontal component, there is a friction force(which the book says is the unbalanced force). NOw why is the engine's force ignored? If it is accounted for, and if it is...
  21. M

    In a clock why does the tip of the hand move faster than somewhere near the centre?

    If you drive in a circle, this friction (which prevents the tires from slipping) will always point towards the centre of that circle. I still dont understand how the friction points toward the centre. look at this rough sketch i made http://tinypic.com/view.php?pic=24np9o5&s=6 the red arrow...
  22. M

    In a clock why does the tip of the hand move faster than somewhere near the centre?

    kk thank you all for your answers. I had another question. I was reading up the chapter. It said when a car moves in a circular way around a bend(With constant ω), the centripetal force is provided by friction. I cannot grasp fully this notion. How does the friction direct inwards toward the...
  23. M

    Question on circular motion, finding out the angular displacement in a clock.

    holy crap, u are right. Its btween 3 and 4.....I totally overlooked that!
  24. M

    Question on circular motion, finding out the angular displacement in a clock.

    Homework Statement A clock is showing 3.30. Calculate the angular displacement in degrees from the 12.00 position of the clock to: i the minute hand ii the hour hand I got my minute answer as 180 degree, which is right. But my second answer was 90 degrees, which apparently is wrong! the...
  25. M

    In a clock why does the tip of the hand move faster than somewhere near the centre?

    This topic is to do with circular motion..angular velocity. I have just begun this chapter in my a2 physics, and I don't really understand why the tip moves faster than the one near the centre. I understand it through calculations(using the different length of radius and then ω/angular...
  26. M

    Is it possible to pursue neuroscience and writing at the same time? Or is it too much

    Hey I am currently in the 12th Standard and want to, become a neuroscientist as well as a writer, however until recently I was thinking about writing later in life(like in my 50s). But recently I have come across various people advising me of the low pay of a neuroscientist, and also with the...
  27. M

    Can anyone tell me the relationship between work done and potential difference?

    I am just an A level student, so have not come across work energy theorem, or friction as resistance...let me show you a question where a application of my question(in MY level) is shown...
  28. M

    Can anyone tell me the relationship between work done and potential difference?

    Can anyone tell me the relationship between work done and potential difference?? CAN ANYONE TELL ME THE RELATIONSHIP BETWEEN WORK DONE AND POTENTIAL DIFFERENCE?? If more work is being done across a component(for ex due to increased resistance), does the pd across it increase or decrease? I...
  29. M

    WHat is the uncertainty in a metre rule?

    WHat is the uncertainty in a metre rule?? For a single value is it 1 mm or is it 1/2mm(half the smallest division) ? And what about measuring something like a length of a stick (we need to take 2 readings, and deduct them like 15-0=15), then is the uncertainty 1+1=2mm or is it .5+.5=1mm ?
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