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  1. P

    Whats wrong with my working

    i thin its just because the question says he puts in 500 a year from 21st to 64th bday so he doesnt put in 500 on his 65th, he only gets interest for that year
  2. P

    Molar volume and molar mass - Need help with 2 Questions

    the equation you need is n = volume / molar volume you need to get n from the mass and put it into the above eqn im pretty sure its in the prelim course
  3. P

    Time payments

    2 years (ie 24 months) have passed since she made the loan interest is not charged on the first 6 months, so is charged on 24-6=18 months which explains the positive term each repayment is made at the end of the year and the loan was made at the start of the year so the first repayment occurred...
  4. P

    help for Complex no.

    \left(e^{\frac{\pi}{2}i}\right)^i=e^{-\frac{\pi}{2}}\\\text{Continuing this you get}\\\pm i \text{ or }e^{\pm\frac{\pi}{2}}
  5. P

    help for Complex no.

    set the first i to e^(i*pi/2)
  6. P

    v=rw questions

    you will only need this for circular motion which you don't do a lot of in hsc
  7. P

    help needed for growth and decay

    You need to separate the variables and integrate \begin{align*}\frac{dN}{dt}&=k(N-P)\\\frac{dN}{N-P}&=kdt\\\ln{(N-P)}&=kt+C\\N-P&=e^{kt+C}\\&=e^{C}e^{kt}\\\text{Let }e^{C}=A\\N-P&=Ae^{kt}\\N&=P+Ae^{kt}\end{align*} For the next part of the question follow these steps: 1. sub in t=0 and...
  8. P

    Projectile Motion Q - Will this ever be in the HSC?

    Although I don't remember this being in the syllabus
  9. P

    Projectile Motion Q - Will this ever be in the HSC?

    Well if we account for the varying mass of the rocket, we use the equation m.dv = -v_g.dm where m is the mass of the rocket (variable) and v_g is the velocity of the gases (500) and v is the velocity of the rocket (variable) dividing by m and integrating you get v_f - v_i = v.ln(m_f/m_i) throw...
  10. P

    Determining a value for the magnetic force constant (k)

    From what I read, I don't think you need to experimentally determine the value of k. I would just take the value 2*10^-7 Tm/A. Also, the equation F=BIl sin(theta) is not relevant here since it applies to the force on a moving charge. What you can do to get B_earth is graph tan(theta) against...
  11. P

    Period of satellite question

    The equation for the period is T = 2pi * sqrt(r^3/GM) which in this case equals 12 If you replaced r with 3r you would have T = 2pi * sqrt(27r^3/GM) This can be rewritten as sqrt(27) * 2pi * sqrt(r^3/GM) which, when you sub in the original value, is sqrt(27) * 12 = 62
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