Friday, October 30, 2015

Velocity Time Graphs (Linear Motion) - Worked Example


  1. A train, which starts its motion from rest, moves along a straight linear road. It  takes a velocity of u by moving with an acceleration of f1 and then a velocity of 3u by moving with an acceleration of f2. After moving with this velocity for a period of uf1, it takes a deceleration of f2 until it comes back to the rest. Show that the total displacement of the train is u2[17f1+7f2]2f1f2.
  2. Answer


    On this graph, OA line segment represent the f1 acceleration and AB represent the f2 acceleration. At BC train moves with a constant velocity and then at CD it decelerate from f2, as described in the question.
    From the given data,
    tanα=f1
    tanβ=f2
    OG =ucotα=uf1
    GF =(3uu)cotβ=2uf2
    ED =3ucotβ=3uf2

    The total displacement = OABCD area
    Total displacement = 12OGGA + 12(AG+BF)GF + BFEF + 12CEED
                                        =12uuf1+3u+u22uf2+3uuf1+123u3uf2
                                        =u22f1+8u22f2+3u2f1+9u22f2
                                        =7u22f1+17u22f2
                                        =u2[17f1+7f2]2f1f2

  3. To be continued... 

Friday, September 11, 2015

Answers For Cambridge AS & A Level P1 (Pure) 2014 (9709/11)



*These answers are only for reference purposes and are not the official marking scheme for the relevant paper. Download Paper

  1. (2+ax)7=7r=07Cr27r(ax)r
    The terms of x and x2 can get by r=1 and r=2 respectively.
    T1=7C1271(ax) and T2=7C2272(ax)2
    7C126a=7C225a2
    a=23
     
  2. Assume θ=tan1(3), Then t=tanθ=3
    sin1(x1)=tan13
    (x1)=sinθ
    (x1)2=sin2θ
    =1cos2θ2
    =11t21+t22
    =1191+92
    =1820
    x1=±310
    x=1±310
    *The answer can be easily taken if you are using table or calculators.
     
  3. 13sin2θ2+cosθ+cosθ=2
    13sin2θ=(2cosθ)(2+cosθ)
    13sin2θ=4cos2θ
    12sin2θ+sin2θ+cos2θ=4
    12sin2θ=41
    sinθ=±12
    θ=300 or θ=1500
     
  4.   
    1. As 4x+ky=20 passes through A(8,4) and B(b,2b),
      4×8+k×(4)=20
      k=3
      4×b+3×(2b)=20
      b=2
       
    2. If the mid point is M,
      M=(8+22,4+42)
      M=(5,0)
  5. If the line y1=2xk meets the curve y2=x2+kx2 at two distinct points, then the quadratic equation y1=y2 must have two distinct roots. For that, the discriminant Δx must be positive.
    2xk=x2+kx2
    x2+(k2)x+k2=0
    Δx=(k2)24×1×(k2)
    But Δx>0
    (k2)24(k2)>0
    (k2)(k24)>0
    (k2)(k6)>0
    either k>2 and k>6 or k<2 and k<6
    So the set of values of k is k>6 or k<2


     
  6.  
    1. Here I show two methods
      Method 01
      OA=3i+2jk and OB=7i3j+k
      AB=AO+OB
      =3i2j+k+7i3j+k=4i5j+2k
      If OAB=900 then the scalar product between OA and AB must be zero.
      OAAB=(3i+2jk)(4i5j+2k)
      =12102=0

      Method 02
      If ^OAB is a right angle, then OAB triangle must be a right angle triangle. So we must be use Pythagorean theorem for the triangle.
      |OA|2=32+22+(1)2=14
      |OB|2=72+(3)2+12=59
      |AB|2=42+(5)2+22=45
      We can see that,
      |OB|2=|OA|2+|AB|2
      Hence, according to the converse of the Pythagorean theorem we can say OAB is a right angle triangle.
       
    2. Area =12×|OA|×|AB|=12×14×45
      Area =3270
       
  7.  
    1. According to the given data,
      S=a(1r)1r  --------- (1)
      3S=a(1(2r))12r ------- (2)
      By dividing (2) by (1),
      3=1r12r    (r, (2r)0)
      36r=1r
      r=25
       
    2. According to the given data,
      T1=7, Tn=84 and T3n=245
      If the common difference is d, then the general term is,
      Tn=a+(n1)d  where a is the first term.
      84=7+(n1)d
      (n1)d=77 -------- (A)
      T3n=a+(3n1)d
      245=7+(3n1)d
      (3n1)d=238 -------- (B)
      Dividing (B) by (A),
      3n1n1=23877
      11(3n1)=34(n1)
      n=23
       
  8.  
    1. When we consider the given figure OA=4cm
      By resolving the side,
      OD=4cosα cm
      The arc length CD=4αcosα   (A=rθ)
      Total perimeter of ABCD=4αcosα+4α+2(44cosα)
      =4α(1+cosα)+8(1cosα) cm
       
    2. Area of a sector =12r2θ
      The area of the shaded region =1242α12(4cosα)2α
      =8π6(1(32)2)
      =13π cm2
       
  9.  
    1. As f(x)=2x2x2 we can get the gradient of the tangent (mT) at P(2,6),
      mT=2(2)222=72
      the gradient of the normal mN satisfies,
      mTmN=1  ( they are perpendicular to each other)
      mN=27
      As the normal passes through point P,
      y6x2=27
      the equation of the normal is 7y+2x46=0
       
    2. By integrating w.r.t x, f(x)dx=f(x)

      f(x)=2x222x2+12+1+c  Where c is a constant
      f(x)=x2+2x+c
      As y=f(x) passes through P,
      6=22+22+c
      c=1
      Then f(x)=x2+2x+1
       
    3. At stationary points f(x)=0
      2x2x2=0
      x31=0
      (x1)(x2+x+1)=0
      As x2+x+10, x1=0
      Therefore there is a stationary point at x=1
      If you substitute two values in positive and negative sides of x=1, to the differential f(x), you will find that this is a minimum. 
      or
      differentiate f(x) w.r.t x again and substitute x=1, you'll get a positive value.
  10.  
    1. x22x15=x22x+(22)2(22)215
      =(x22x+1)16=(x1)216
       
    2. f(x)=(x1)216
      c is the minimum value that can be taken for f(x)
      fmin(x)=016=16(0 is the minimum value for a quadratic)
      cmin=16
       
    3. If f(x)c then xp
      9=(p1)216
      (p1)2=25
      p1=±5
      p=6  as p is a positive constant
      65=(q1)216
      (q1)2=81
      q1=±9
      q=10 as q is positive.
       
    4. y=f(x)=(x1)216
      (x1)2=y+16
      x1=±y+16
      x=1±y+16
      0<x and 9<y
      f1(x)=1+x+16
       
  11.  

    1. By differentiating both curves w.r.t x, at the point Q(2,3), we can get the gradient of to tangents.
      m1=ddx(4x+1)|x=2=12(4x+1)1214|x=2
      m1=24×2+1=23
      m2=ddx(12x2+1)|x=2=122x|x=2
      m2=2

      θ=θ2θ1
      tanθ=tan(θ2θ1)
      tanθ=tanθ2tanθ11+tanθ2tanθ1
      tanθ=|m2m11+m2m1|
      θ=tan1|2231+223|
      θ=tan1(47)=29.7450
       
    2. Area =20y1y2dx
      =204x+1(12x2+1)dx
      =[(4x+1)12+112+11412x33x]20
      =[(4x+1)326x36x]20
      ={(4×2+1)3262362}{(0+1)32600}
      =93/2686216
      =1 unit
Stay connected for the next paper....

Thursday, September 10, 2015

Centers of a Triangle

Triangle is an important polygon when we consider the geometry. It has several properties which are very specific to the triangle. In this article I have mentioned about the centers of a triangle.


  1. Centroid

    Centroid is the point that the three medians of triangle meet together (concurrent). Following figure shows the geometry of the centroid. (median is the line, which joins the vertex and opposite mid point)

    Centroid is the center of gravity of a triangle and we can discuss it in the lesson "Center of Gravity".
    Here AG:GE=BG:GF=CG:GD=2:1
    GE=13AE
  2. Circumcenter 

    Cercumcenter is the center of the circumscribed circle of a triangle. Concurrent perpendicular bisectors of each side of a triangle gives the circumcenter. 

    Here AM=BM=CM= Radius of circumcircle. The angle subtend the center is equal to the double of the angle which subtend the circumference. So AMB=2ACB=2C.

  3. Incenter

    Incenter is the center of the inscribed circle of a triangle. This is the concurrent point of three angle bisectors. The circle drawn with incenter as the center and the perpendicular length from incenter to the sides(which is equal) as the radius, is called the incircle.

    ID=IE=IF= Radius of incircle.
  4. Orthocenter

    Orthocenter of a triangle is the concurrent point of three altitudes. (altitude is the line drawn from a vertex to the opposite side, perpendicularly). Refer the following figure.
  5. Nine point circle
    Nine point circle is the circle which goes through three mid points of sides, three feet of altitudes and three mid points of line segments from orthocenter to the vertices.

    Radius of circumcircle is two times the radius of nine point circle.
Note: There are other centers and lines (such as Euler line) specific to the triangle. Here I have described most important properties.

Wednesday, September 9, 2015

Trigonometry 02 (Measurements of Angles & Trigonometric Ratios)

  • Definition of Angle

Let's assume that the line OP is rotating in the same plane, around the point O as shown in the figure. Let its origin is OA and it is getting on to the positions OB,OC,OD... respectively. Then we measure the angle between OA and any position of OP such as OB, using the amount of rotation that it made during its relocation from OA to OB. According to this, there can be any number of complete rotations through OA, when OP comes to OB. 


So not as in Geometry, in Trigonometry there can be any magnitude for the angles, without limitations. According to the above figure O is the Origin, OA is the Initial Line and OP is the Rotating Line (Generating Line/ Radius Vector).

  • Measurement of angles

Measuring the angles has happened in ancient history as well. For the measurement of angles we use the unit of complete revolution; that is the angle of a complete cycle which subtend the center of a circle. This complete angle has divided in to 360 equal parts and has called them degrees, by the ancient astronomers.

  • Sexagesimal measurement 

In this measuring system, angle in a complete cycle has divided into four equal parts and has named them as right angles. Each right angle has divided into 90 equal parts and has introduced each part as a degree, and again each degree has divided into 60 equal parts and called each part as a minute. Finally each minute has divided again into 60 equal parts and named them as seconds.
The angle which describe as 54 degrees, 45 minutes and 3.45 seconds, can be denoted by 540 45 3.45.

  • Radian measurements

Practically we use the above mentioned sexagesimal system for measuring angles. But in theoretical applications radians are used widely for measuring angles. A radian has defined as the angle which subtend the center by an arc, having the length of the radius of the particular circle.
AOB=1rad



  • The ratio between the circumference and the diameter, is a constant in any circle. 


To derive this, we have to consider the circle as a polygon with n number of sides. Consider two circles with radii r1 and r2 and centers O1 and O2.

If we consider these two are regular polygons and assume the length of a side of the first polygon is A1B1 and the length of a side of the second polygon is A2B2.
So A1O1B1=A2O2B2=3600n.
Hence both triangles A1O1B1 and A2O2B2 become equi-angular.
A1B1O1A1=A2B2O2A2
Let A1B1=l1 and A2B2=l2, then,
l1r1=l2r2
nl1r1=nl2r2
If the number of sides n is going to be increased infinitely, then nl1 tends to be the circumference of the circle with radius r1. Same thing happens to the other circle as well. If the circumferences of circles are C1 and C2 respectively then,
C1r1=C2r2
This shows us that the ratio between the circumference and the radius of any  circle is a constant. If so, the ratio between the circumference and the diameter of any circle is probably a constant.
circumferencediameter is a constant.
This constant is represented by the Greek letter π. The value of this constant is approximately equal to the 227. However exact constant is an Irrational number.
Circumference C=2πr 

  • Radians and Degrees

As we know the angle that  subtend the center of a circle by a complete cycle is 3600. According to the definitions of a radian,
Subtend angle by a r arc length =1 rad
The angle of a complete cycle =1r2πr     (C=2πr)
3600=2π rad
1 rad=36002π57018

  • Length of an arc that subtends the center by a θ angle.

To be continued...

Sunday, September 6, 2015

Trigonometry 01 (Useful Formulas in Trigonometry)



  1. S=rθ  [Arc = Radius × Angle in radians]
  2. Area of a sector A=12r2θ
  3. Fundamental identities of trigonometry
    • cos2θ+sin2θ=1
    • 1+tan2θ=sec2θ
    • cot2θ+1=cosec2θ

  4. θ
    00
    300
    450
    600
    900
    1800
    sinθ
    0
    12
    12
    32
    1
    0
    cosθ
    1
    32
    12
    12
    0
    1
    tanθ
    0
    13
    1
    3
    0
     
  5. sin(900θ)=cosθ
    cos(900θ)=sinθ
     
  6. sin(θ)=sinθ
    cos(θ)=cosθ
     
  7. sin(1800θ)=sinθ
    cos(1800θ)=cosθ
     
  8. sin(900+θ)=cosθ
    cos(900+θ)=sinθ
     
  9. sin(1800+θ)=sinθ
    cos(1800+θ)=cosθ
     
  10. sin(A±B)=sin(A)cos(B)±cos(A)sin(B)
    cos(A±B)=cos(A)cos(B)sin(A)sin(B)
     
  11. sin(2A)=2sin(A)cos(A)
     
  12. cos(2A)=cos2(A)sin2(A)=2cos2(A)1=12sin2(A)
     
  13. tan(2A)=2tan(A)1tan2(A)
     
  14. sin(3A)=3sin(A)4sin3(A)
     
  15. cos(3A)=4cos3(A)3cos(A)
     
  16. tan(3A)=3tan(A)tan3(A)13tan2(A)
     
  17. sinC+sinD=2sin(C+D2)cos(CD2)
     
  18. sinCsinD=2cos(C+D2)sin(CD2)
     
  19. cosC+cosD=2cos(C+D2)cos(CD2)
     
  20. cosCcosD=2sin(C+D2)sin(DC2)
     
  21. 2sinAcosB=sin(A+B)+sin(AB)
  22. 2cosAsinB=sin(A+B)sin(AB)
  23. 2cosAcosB=cos(A+B)+cos(AB)
  24. 2sinAsinB=cos(AB)cos(A+B)
     
  25. If sinθ=sinα, then θ=nπ+(1)nα
    If cosθ=cosα, then θ=2nπ±α
    If tanθ=tanα, then θ=nπ+α
    Here nZ
     
  26. For an ABC triangle, in the standard notation,
    1. sinAa=sinBb=sinCc
    2. cosA=b2+c2a22bc
    3. a=b cosC+c cosB
    4. tan(BC2)=(bcb+c)cotA2
    5. cosA2=s(sa)bc
      Here s is the double of perimeter, of the ABC triangle (2s=a+b+c)