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  1. 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
  2. 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...
  3. 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...
  4. 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...
  5. 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...
  6. 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...
  7. 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...
  8. 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...
  9. 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 ?
  10. M

    If tan x = k(where k is a positive constant),How is tan( pie/2 − x)=1/k

    Homework Statement The exact question is in question one part ii of Homework Equations The Attempt at a Solution For the first one I just pluged in a value for...
  11. M

    ANyone know how to draw a parallelogram/triangle to resolve force?

    ANyone know how to draw a parallelogram/triangle to resolve force?? Homework Statement question 1b Homework Equations The Attempt at a Solution I drew...
  12. M

    Chemistry 1 mark mcq question on enthalpy change of atomisation of hydrazine? help!

    Homework Statement Hydrazine was used as a fuel for the Messerschmidt 163 rocket fighter in World War II and for the American Gemini and Apollo spacecraft. What is the enthalpy change of atomisation of 1 mol of gaseous hydrazine? A 550 kJ B 1720 kJ C 1970 kJ D 2554 kJ Use of the...
  13. M

    What is the percentage by mass of phosphorus in the fertiliser? AS level MCQ

    Homework Statement A garden fertiliser is said to have a phosphorus content of 30.0% ‘P 2 O5 soluble in water’. What is the percentage by mass of phosphorus in the fertiliser? A 6.55% B 13.1 % C 26.2% D 30.0% Homework Equations The Attempt at a...
  14. M

    A Haunting question on diffraction grating!

    Homework Statement This question is pretty interesting, but a bit long, so bear with me question 5 part c For (i) The width of each slit is increased but the separation remains...
  15. M

    Can sodium chloride be categorised as a giant molecular structure

    I was attempting this question where I had to say which, out of graphite, diamond and sodium chloride represent a giant molecular structure? The answer is only the first two. Why is the latter excluded?
  16. M

    Diffraction grating sum, 1 mark mcq question (a level)

    Homework Statement Im having a bit trouble with diffraction gratings lately, with sums like this: A parallel beam of light of wavelength 450 nm falls normally on a diffraction grating which has 300 lines /mm. What is the total number of transmitted maxima? A 7 B 8 C 14...
  17. M

    1 mark question on kinematics, or a stone fallin through air.

    Homework Statement A stone is dropped from the top of a tower of height 40 m. The stone falls from rest and air resistance is negligible. What time is taken for the stone to fall the last 10m to the ground? A 0.38s B 1.4s C 2.5s D 2.9s Homework Equations The Attempt at a...
  18. M

    Which one of the nuclei below completes the acceleration with the lowest speed.1mark

    Homework Statement question 40 Homework Equations The Attempt at a Solution I got D, because the heaviest should have the lowest speed. But I am wrong. dnt know why
  19. M

    1 mark question on application of components and workdone(gravitanal potential energy

    Homework Statement question 14 Homework Equations mgh=gpE fxd=workdone The Attempt at a Solution I HAVE NO IDEA WHY MY ANSWER IS WRONG!! AND THIS IS GETTING ME so...
  20. M

    A one mark moments question (a see saw,pivot type sum, prolly easy) in A level MCQ

    Homework Statement question 12 Homework Equations moments=Fd The Attempt at a Solution 60X20=50d d=24cm
  21. M

    Interesting question on functions(domain and range) but can't understnd the answer

    The question is from question no. 7 (i). I think it should be more than easy for a functions fanatic( or someone who does math regularly for that matter) to get the right answer, but...
  22. M

    I dont understand how to calculate percentage uncertainty?

    I dont understand how to calculate percentage uncertainty!? I know in chem we calculate uncertainties by smallest division/the reading X 100. But in physics i am clueless. For instance heres an example The power loss P in a resistor is calculated using the formula P = V^2/R. The uncertainty...
  23. M

    A normal distribution problem, AS level, on tyres! Need help in the last part.

    Homework Statement question no. 6 part ii (Safety regulations state that the pressures must be between 1.9 − b bars and 1.9 + b bars. It is known that 80% of tyres are within...
  24. M

    Combination problem: A football team consists of 3 players who play in a defence

    combination problem: A football team consists of 3 players who play in a defence.... Homework Statement 7 a ii (if exactly one forward player must be included, together with any...
  25. M

    Question on permutation and combination(girls and boys standing in a line)

    Homework Statement question 6 b ii Homework Equations The Attempt at a Solution The concept is bothering me. the answer is 5! × 3! × 4C1. Why is it a permutation problem? Plus...
  26. M

    Neurology or Neuroscience? Plus how much is a neuroscientist paid?

    I can;t decide between trying for neurology or neuroscientist. All though I think neuroscientist would be a more interesting job, I do not like maths or chemistry( I love Bio and Physics). Being a neurologist would not only be satisfying aswell, but it will also pay aLOT! But the time of MBBS...
  27. M

    Suggestion Make a career section,for those who have trouble identifying the course they'l pursue

    I want to be a neurologist in India. However it is horribly difficult to analyse all the courses involved and degrees needed to practise, through the net. It is frankly because there is hardly anybody with the correct knowledge and those with the knowledge hardly reply. I just want a basic blue...
  28. M

    With which sample(s) of halide does sulphuric acid act as an oxidising agent?

    Concentrated sulphuric acid is added to separate solid samples of sodium chloride, sodium bromide or sodium iodide. With which sample(s) does sulphuric acid act as an oxidising agent? A sodium chloride only B sodium chloride and sodium bromide C sodium bromide and sodium iodide D...
  29. M

    Chemistry Question regarding empirical formula and molecular formula(finding 2 variables)A Lvel

    Homework Statement question 10 Homework Equations The Attempt at a Solution The way I am doing it, is to get two equations in terms of x and y and then equate them. For the...
  30. M

    How do I find the spacing(d) of a grating in a diffraction grating experiment.

    Homework Statement question no. 7b Homework Equations dsin∅=nλ The Attempt at a Solution I subtracted the two angles and got 26 degrees. So then I plugged...