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AravindG

  • 5 years ago

wel i hav some doubts on 1d motion pls cm here

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  1. AravindG
    • 5 years ago
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    1.how can i understand how acceleration and displacemenyt varies from a displacement time graph??

  2. AravindG
    • 5 years ago
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    srry accleration and velocity i meant

  3. AravindG
    • 5 years ago
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    based on that tell me hw the sign in varous intervals OA ,,AB ,BC and CD is -, 0 ,+ ,0

  4. AravindG
    • 5 years ago
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    |dw:1327309166279:dw|

  5. anonymous
    • 5 years ago
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    Imagine a simple case of a parabolic x vs. t graph. We find that the equation of the line on the graph is\[x = 10 t^2\]As would be the case in constant acceleration. Now, we know that velocity is defined as the change in distance over the change in time. In differential form this is\[v = {dx \over dt}\]And additionally, that acceleration is the change in velocity over the change in time. Again, in differential form, this is\[a = {dv \over dt} = {d^2 x \over dt^2}\] It can readily be seen, that to find the velocity of the above displacement equation, we simply differentiate with respect to time. \[v = 20 t\]and then differential the velocity with respect to time to find the acceleration.\[a = 20\]

  6. AravindG
    • 5 years ago
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    i mean sign of acceleration

  7. AravindG
    • 5 years ago
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    eashmore i asked how we can evaluate from the graph

  8. AravindG
    • 5 years ago
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    look the graph

  9. anonymous
    • 5 years ago
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    There are infinite possibilities to your second question. But since we have observed that \[a = {d^2 x \over dt^2}\]it is apparent that acceleration is the second derivative of the x vs. t curve.

  10. anonymous
    • 5 years ago
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    My method still holds. Use the principles you learned in Calculus and the above differentials to draw conclusions.

  11. AravindG
    • 5 years ago
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    2.|dw:1327309473228:dw|

  12. AravindG
    • 5 years ago
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    here its a smooth in clined planethe time taken to reach bttom is sqr(2l/g)

  13. AravindG
    • 5 years ago
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    i dont understand why we can use s=1/2gt^2 directly here

  14. AravindG
    • 5 years ago
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    ipls help

  15. AravindG
    • 5 years ago
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    but the answer is sqr(2l/g)

  16. AravindG
    • 5 years ago
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    we just applied equaion of motion just as usual why??

  17. AravindG
    • 5 years ago
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    |dw:1327309719031:dw|

  18. AravindG
    • 5 years ago
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    it is said that acceleration of A and B are in ratio tan 60 to tan 30 how????

  19. AravindG
    • 5 years ago
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    helo pls help

  20. anonymous
    • 5 years ago
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    Patience....

  21. AravindG
    • 5 years ago
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    k

  22. anonymous
    • 5 years ago
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    Lines A and B have no acceleration. They are constant velocity plots. The second derivative of a straight line is zero.

  23. AravindG
    • 5 years ago
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    are u sure?/

  24. anonymous
    • 5 years ago
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    If that is a displacement vs. time graph, and lines A and B are straight, then yes, I'm 100% sure.

  25. AravindG
    • 5 years ago
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    y is a=0??

  26. anonymous
    • 5 years ago
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    I told you why. Because the second derivative of a straight line is zero.

  27. AravindG
    • 5 years ago
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    k tel me the othr one

  28. anonymous
    • 5 years ago
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    I don't think it is right either. The time it takes to reach the bottom will be\[T = \sqrt{2l \over g \sin(\theta)}\]

  29. anonymous
    • 5 years ago
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    yea i agree with that t=sqrt(2l/g sin theta)

  30. AravindG
    • 4 years ago
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    but it is not there in options

  31. AravindG
    • 4 years ago
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  32. anonymous
    • 4 years ago
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    Let's analyze the equations of motion here. The only force acting on the particle moving down the incline is that of gravity. Therefore, we can say with certainty that\[\vec a = -g\]From the definition of acceleration, we can also say that\[\vec a = { d \vec v \over dt}\]Separating variables\[d \vec v = \vec a dt\]Integrating\[\int\limits d \vec v = \int\limits \vec a dt \rightarrow \vec v = \vec a *t\]By the same token, we can observe that\[\vec s = \vec v_0*t+ {1 \over 2} \vec a *t^2\]Take careful note of the fact that displacement, velocity, and acceleration are vector quantities. Now, let's analyze the kinematics of the problem. Let's fix a frame such that \(\hat i\) is directed from the top of the incline to the bottom and parallel to the inclined surface, \(\hat j\) is directed away from the inclined surface and perpendicular to the inclined surface, and \(\hat k\) is \(\hat i \times \hat j\). We will also fix a ground, inertial frame with unit vectors \((\hat I,\hat J,\hat K)\)|dw:1327390446864:dw|Observe that the direction cosines are \[\left(\begin{matrix}\hat i = \cos(\theta) \hat I - \sin(\theta) \hat J \\ \hat j = \sin(\theta) \hat I + \cos(\theta) \hat J\end{matrix}\right)\]Let's also observe that\[\vec a = -g \hat J\]and, from the above direction cosines, that\[\vec a = g \sin(\theta) \hat i\]The particle will move along the inclined plane with a displacement of \[\vec s = l \hat i\]From the equation I gave earlier for displacement, we can observe that\[l \hat i = \vec v_0 \hat i * t + {1 \over 2} g \sin(\theta) \hat i * t^2\]Simplifying by observing that \(v_0 = 0\), and that \(\hat i\) cancels out through all terms, we get\[l = {1 \over 2} g \sin(\theta) \cdot t^2\]Solving for \(t\)\[t = \sqrt{ 2l \over g \sin(\theta)}\]This isn't an answer choice, so let's see if we can manipulate it to match one of the answers. Observe from trigonometry that\[\sin(\theta) = \frac{h}{l}\]Solving for \(l\)\[l = {h \over \sin(\theta)}\]Let's substitute this into our expression for \(t\), yielding\[t = \sqrt{2 h \over g \sin^2(\theta)}\]Removing \(\sin(\theta)\) from the radical yields, \[t = \arcsin(\theta) \sqrt{2 h \over g}\]which appears to be answer choice c.

  33. AravindG
    • 4 years ago
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    hey i got the answer but there is no arc sin theta

  34. anonymous
    • 4 years ago
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    \[\arcsin(\theta) = {1 \over \sin(\theta)}\]

  35. AravindG
    • 4 years ago
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    lol

  36. AravindG
    • 4 years ago
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    k i got it ithought it was sin inverse

  37. anonymous
    • 4 years ago
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    \[\arcsin(\theta) = {1 \over \sin(\theta)} = \sin^{-1}(\theta)\]

  38. AravindG
    • 4 years ago
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    hey thts not

  39. AravindG
    • 4 years ago
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    1/sin theta is cosec theta

  40. anonymous
    • 4 years ago
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    Yeah. You're right.

  41. anonymous
    • 4 years ago
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    Just pretend like it is here.

  42. AravindG
    • 4 years ago
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    :)

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