Recent content by jiboom

  1. J

    Shm question -- a mass hanging on a spring vertically set into motion

    Yes the b should be as in your reply. To find b ill use frequency is 1/period Are my conditions correct, ie H is 2 at t is 0? Thanks
  2. J

    Shm question -- a mass hanging on a spring vertically set into motion

    A mass on the end of a spring which is hanging vertically is raised up and let go. It then oscillates between 2m and 1.5m above the floor and completes 32 cycles in one minute. The height, h metres, of the mass above the floor after t seconds can be modelled by the function h=acos(pi t / 180)...
  3. J

    Centroid question

    not heard of the washer method. i know the formula for x bar for a hemisphere but the question wants it from integration
  4. J

    Second moment of area

    as in my first post, i am trying to find the second moment of area about the vertical axis
  5. J

    Centroid question

    7) Pile foundations are the part of a structure used to carry and transfer the load of the structure to the bearing ground located at some depth below ground surface. A concrete pile for a domestic dwelling has a radius of 1000 mm at its base, and 2000 mm at the top. It is 2000 mm deep and...
  6. J

    Second moment of area

    almost, the picture i have has the circle more towards the rhs of the rectangle.
  7. J

    Second moment of area

    Find the second moment of area about the vertical axis for the cross-section of the follwing shape. i cant get the pic to paste so will describe it: it is a rectangle of horizontal length 8 and vertical height 6. if we let (0,0) be at the lhs bottom corner, then a circle has been cut...
  8. J

    Centre of mass question

    i am such an idiot!! I put the point on BC and not AP!! your post made me scratch my head when you mention a right angle triangle! this led me to discover i had the wrong point!! DOH i now have answer as i get the quadratric i was after :) thanks
  9. J

    Centre of mass question

    i know ABC is 90. the triangle left is not a nice one which is why i am saying com of APC can be worked using com of APC and ABP which as they are right angled i know com is 1/3 of the distance of base and height from right angle. then as i dont care where on BC just that it is on BC i let x...
  10. J

    Centre of mass question

    anyone else want to join in and lend a hand? i seem to have lost nopoke
  11. J

    Centre of mass question

    ok,ill try and outline my idea a bit better/. consider the shape with APC cut out. i know BG (G=com) is vertical if shape is suspended at B. if BC is vertical then G lies on BC then the shape has com (0,y bar) if i measure from B so i need to find the com off the new shape and set the...
  12. J

    Centre of mass question

    a triangle ABC with AB=BC=2a and AC=2a rt(2) is drawn on a uniform lamina. A semi-circle is drawn on BC as diameter,on the opposite side of BC from A and the area enclosed by the triangle and the semi-circle is cut out. The resulting lamina is suspended freely from B,show that AB makes an angle...
  13. J

    Motorboat relative motion

    cheeky bump/ having a lot of trouble with rel motion agaisnt a current. got all other questions in the exercise but these allude me. my methods must be ok if im getting the non current questions right so only need a nudge in right direction.
  14. J

    Motorboat relative motion

    a motorboat moving at 8km/h relative to the water travels from A to a point B 10km whose bearing from A is 150. it then travels to C,10km from B and due west of B. if there is a current of constant speed 4km/h from north to south,find the 2 courses to be set. having a bit of trouble with...
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