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  1. E

    Mathematics: Post your doubts here!

    b) Having two sides be the same makes it an isosceles triangle 360 = 66 + 2x C) ADE and EFC are equal (alternate angles) ECF you already have FEC and AED are equal
  2. E

    Chemistry: Post your doubts here!

    K+ has one more electron shell than Na+ K+: 2,8,8 Na+: 2,8 As you go down the group, both the ionic and atomic radii increase.
  3. E

    Mathematics: Post your doubts here!

    This makes sense?
  4. E

    Mathematics: Post your doubts here!

    What are the answers? Is alpha = 1.23?
  5. E

    Mathematics: Post your doubts here!

    Was your answer to the first part y = 70e^[e^(-3t) - 1] ? As t goes to infinity, e^-3t tends to zero thus, y tends to 70e^[0 - 1] = 70e^-1 so we have: yFinal = 70e^-1 yStart = 70 (from main question) p = (yFinal/yStart)*100 p = 100e^-1
  6. E

    Mathematics: Post your doubts here!

    (i) It being a one mark question is a hint at a clever solution: (ii) From main diagram: AreaTotal = 2*AreaB + AreaCircle (or 2*AreaSemiCircle) AreaA = (i) - AreaB
  7. E

    Physics: Post your doubts here!

    Answer is C Why is D right but not C?
  8. E

    Physics: Post your doubts here!

    This diagram shows how the superposition of an incident and reflected wave results in a stationary wave. The waves never have opposite displacements at the antinodes, so it can't be A.
  9. E

    Physics: Post your doubts here!

    No problem :)
  10. E

    Physics: Post your doubts here!

    Q22. The gradient of displacement-time graph is velocity, so when the gradient is zero the velocity and thus KE are also zero. The gradient is zero at time = 0, 0.5T, T, 1.5T and 2T So the KE must be zero at those time coordinates too, only graph D shows this. Q14. F is the force provided by...
  11. E

    Physics: Post your doubts here!

    Q21. According to principle of conversation of momentum : Total momentum before emission (P1) = Total momentum after (P2) P1 = o (stationary) The nucleus emits one proton, so the daughter nucleus will have a nucleon number of A- 1. It's mass will be (A-1)m, where m is the mass of one nucleon...
  12. E

    Physics: Post your doubts here!

    Q26. Taking velocity to the right as positive gives: Total P = (2m)(u) - (m)(u) = mu A) (m)(5u/3) - (2m)(u/3) = mu B) (m)(2u/3) - (2m)(u/6) = mu/3 C) (m)(2u/3) + (2m)(u/6) = mu D) (3m)(u/3) = mu Only B doesn't follow the principle of conversation of momentum.
  13. E

    Chemistry: Post your doubts here!

    Imagine a line through the double bond in D, see how the previously double bonded carbon atoms are attached to the same group? both will form 2-methypropanoicacid. While in B they are attached to different groups.
  14. E

    Chemistry: Post your doubts here!

    q22. Sketch the products when the hot Mno42-/H+ breaks the double bonds: A) forms an acid and a ketone B) forms two different acids C) forms a dicarboxylic acid (two co2h gps attached to the same molecule) D) forms two acids but they have the same formula answer is B
  15. E

    Chemistry: Post your doubts here!

    q18. A) NH4+ does not NH3 B) NH3 is the one that accepts the H+ C) Changes from 107 in NH3 to 109.5 in NH4+, since NH4+ has a tetrahedral arrangement D) This is the correct answer. H+ doesn't have any electrons, the bond is dative Look at the mechanism to understand this better. q4. Only C has...
  16. E

    Chemistry: Post your doubts here!

    Write the equations to get the amount of O2 needed for one mole of each element: Mg + 1/2 O2 → MgO Al + 3/4 O2 → 1/2 Al2O3 S8 + 12 O2 → 8SO3 So its 0.5, 0.75, 12.
  17. E

    Chemistry: Post your doubts here!

    Which fertilisers, when washed out of soil by rain, cause excessive growth of river plants and algae with the result that fish in the river die? 1 K2SO 4 2 NH4NO 3 3 NaNO3 Only 2 and 3 are correct. Won't the K+ ions in 1 also cause excessive growth in plants?
  18. E

    Chemistry: Post your doubts here!

    oct nov 2008 Q 38. Which of the following would be suitable for use in a fire extinguisher? 1 CBrF 3 2 CH3(CH2)5CH2Br 3 HCl Only statement 1 is correct, how come 2 isn't?
  19. E

    Physics: Post your doubts here!

    Either one works
  20. E

    Physics: Post your doubts here!

    In the final answer you should use the same number of sigfigs as the value with the smallest number of sigfigs in your calculation. Example: m = 1.90 kg (3sf) v = 2.3 ms^-1 (2sf) The kinetic energy here should have 2sf.
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