Search results

  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...
  15. J

    General motion of a particle

    great,thanks for your time with this.
  16. J

    General motion of a particle

    maybe an easier question would be to clear up what the w is in the question so from R=(2coswt,2sinwt) is the w the same as |w| the angular speed? if so,is it just to be assumed its a number and not a function of some variable such as time as it's not writtem w(t)?
  17. J

    General motion of a particle

    hi,thanks for coming back. forget the a,the letter used in the question was omega. i know what |V| is,it is just 2omega but.... if this omega (a in my original post) is the angular speed i cant say |v| is constant UNLESS i know omega in the question is constant? maybe i should...
  18. J

    General motion of a particle

    ∂ hi. dont give up on me just yet :) i do appreciate your help and just need one last shove to get there. all i need convincing off now is that the omega=angular speed =|v| is constant. does this follow from the question? if this is so,then for sure i am happy |v|=constant =>...
  19. J

    General motion of a particle

    as i say |v|=2ω, but if ω is the angular velocity then i cant say this is constant without assuming what i want to prove. i should say,i have changed that a in my op to ω as that is the letter the question uses.
  20. J

    General motion of a particle

    im afraid im totally lost here. v = |v| is equal to 2ω so how are you saying this is constant? im trying to show ω is constant which you seem to be saying,forgive me if im misunderstanding, is equal to ω so i dont see how the constancy of v follows without assuming what im trying...
  21. J

    General motion of a particle

    tiny-tim has gone off-line. can you help explain what they were getting at?
  22. J

    General motion of a particle

    i see what you are saying but im thinking along these lines: ω =ω then how can i then say |v| is constant? |v| is 2ω so is only constant if ω is but that is what im trying to show and i dont understand v = ω x r lhs is a vector,but rhs is vector product of 2 scalars ?
  23. J

    General motion of a particle

    lol. wont be sleeping til i get this. i dont have much here to play with. v=rω now is ω angular velocity or angular speed? the v i have is not angular velocity and not constant r is 2 now in your first post you said to use v=rω but then i just get r=2 so that does not show...
  24. J

    General motion of a particle

    so what do i need to say to justify angualr velocity is constant?
  25. J

    General motion of a particle

    sorry but im now confused again. the question actually says x=2cosωt y=2sin ωt so V=V=[-2ωsin(ωt),2ωcos(ωt)] so |V|=2ω so using v=rω only gives me r=2????
  26. J

    General motion of a particle

    think im being thick. is it that as angular velocity only depends on the angle we have |ω|=ω just as v=|v| for 1-d motion
  27. J

    General motion of a particle

    now you point it out, yes it is:) i was going to use v = rω but as i am taking |v| am i not just getting angular speed not velocity?
  28. J

    General motion of a particle

    a particle moves in the xy plane such that at a time t it is at a point (x,y) where x=2cos(at) y=2sin(at) prove particle moves in a circular path with constant angular velocity. prove that the acceleration of the particle at time t is in the direction of the radius from the particle to...
Top