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anthropos

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Posts posted by anthropos

  1. That includes checking teh credentials of teh author and...and... o_o is a book considered reliable if the publication date is seven years from now (2000(? The book I am referring to is a medical book called Vaccination: the facts, the fears, the future by Gordon Ada. Are there any more factors that can decide whether a book is reliable?

  2. The first two terms of a geometric progression are x and y where -x < y < x (<--what does this mean?) If the sum of the first n terms is equal to the sum to infinity of the remaining termsm prove that x^n = 2y^n.

     

    So I did this.

     

    T1 = x = a

    T2= y

    r= y/x

    Tn+1 = y^n

    ...

    x(1-(y/x)^n) = y^n (after substituting a and r values into G.P formulae)

    But i don get the answer! what's the prob?

  3. g(x) = ln (x-2), x>2 (x is a real number)

     

    The question says find g inverse. I have no problem finding the function, but I met difficulty in looking for the domain. The domain of g inverse is the range of g, but I cannot find the range of g, so do we have to state the domain of g inverse?

  4. A purse at radius 2.00m and a wallet at radius 3.00m travel in uniform circular motion on the floor of a merry-go-round as the ride turns. They are on the same radial line. At one instant, the acceleration of the purse is (2.00 m/s2) i +(4.00 m/s2)j. At that instant and in unit-vector notation, what is the acceleration of the wallet?

     

    Can somebody give me some hints on how to tackle this question? What is the relation between the radius of the individual items and their acceleration? I just started on this topic yesterday. =.=

  5. Yo, I am a 17 year old student and one day I saw this question in my textbook.

     

    "Acids are added to cola drinks to lower the pH to about 2.5 to impart tartness. Show that a cola that contains from 0.057 to 0.084% of 75% phosphoric acid (H3PO4), by mass, meets this pH requirement. "

     

    Can somebody explain the "0.057 to 0.084% of 75% phosphoric acid (H3PO4), by mass"? I don't quite get it.

  6. Yo, i am a 15-year-old student. One day I saw this in my assignment.

     

    A car of mass 1500 kg accelerates from rest at 5.00 m/s2 for 5.00 s on a straight road. Find teh minimum power needed for the engine to achieve this task.

     

    The answer they gave was

     

    Power = work done/time

    = 1/2 mv2 / t

    =1/2 m(u+at)2 / t

    =1/2(1500)(0+5x5)^2 / 5

    =93750

    =93.8W

     

    But my answer was

     

    Since m=1500 kg

    u=0

    a=5.00 m/s2

    t=5.00s

    F=ma=1500x 5.00 = 7500N

    v=u +at =5.00 x 5 =25m/s

    P=Fv ==> 7500x25 = 187500 = 187.5 kW

     

    Not only the answer is wrong, 187500 is twice as 93750. What happened? Please enlighten me! Thanks. ;)

  7. Yo, I am a 16-year-old student who struggles with probability. Pardon my grammar.

     

    A bag contains 8 green and 4 red balls. 6 balls are drawn at random in succession from the bag without replacement. What is the probability that the colours appear alternately?

     

    Does this question require a probability tree? Do tell me if it does, because we have to choose 6 balls and I think it is too complicated for one. So on seeing that it is "without replacement", I just did this.

     

    G R G R G R => 8/12 x 4/11 x 7/10 x 3/9 x 6/8 x 2/7 = 2/165

    R G R G R G => 4/12 x 8/11 x 3/10 x 7/9 x 2/8 x 6/7 =2/165

     

    And then I add them up because they are mutually exclusive events.

     

    I got 4/165 which is terribly wrong because the answer is 16/33.

     

    What went wrong? The whole solution is porbably wrong because i haven't fully understood probability though I have tried very hard to. Somebody kind enough please enlighten me! Thanks :D

  8. Hullo, I am a 16-year-old. This is a question in my assignment.

     

    A student said that a piece of paper would fall on the ground when released because the atmospheric pressure forced the paper to fall down. Use the kinetic theory to determine whether the above statement is true.

     

    So my answer is (Pardon my grammar. i know it's bad)

     

    The above statement is false. The volume of fixed mass of air on the upper and lower sufaces of the paper is the same. This means that the number of air molecules moving around per unit volume of space is the same on the top of and below the paper. The frequency of collision between air molecules and the two surfaces of the piece of paper is the same, so equal amount of force is exerted per unit area of the paper for the same period of time. Thus the pressure of the air (atmospheric pressure) on top of and below the paper is the same. Unless the pressure on either side of the paper of the air is higher than that of the other side will the paper be forced to move in a certain direction which is impossible in reality, because atmopsheric pressure is generally constant. The real reason why a piece of paper would fall on the ground is because of gravitational force pulling towards the ground.

     

    Is the statement true? Is my explanation correct? Please tell me to edit parts which you think that is wrong or could have been better. Just that. Thanks. :P

  9. (I am a 9th grade student. :D) Acidified potassium dichromate (VI) is used to test for the presence of reducing agents. How do I derive the 6 electrons in the following ionic equation during which the test of a reducing agent like sulphur dioxide is carried out?

     

    Cr2 O7 2- (aq) + 14H+ (aq) +6e- ==> 2Cr3+ (aq) + 7H2O (l)

     

    How is dichromate (VI) ion reduced to chromium (III) ion? :confused:

     

    Cr2 O7 2- ---> 2Cr 3+

     

    How can reduction result in a negative charge changed to a positive charge?

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