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    hi so I was doing the summary questions for 18.3 and stuck on question 2 ( as follows)

    the displacement of an object oscillating in simple harmonic motion varies with time according to the equation x (mm) = 12cos10t where t = time in seconds after the object was at max positive displacement.

    so for a (i) it said to calculate amplitude which I got as 12mm.
    a (ii) was to find time period which I got as 0.6283185307 a
    question (b) states what will by the displacement of the object when t = 0.1

    I put t = 0.1 in the equation and got 11.99817234 mm

    but the answer at the back says 6.5 mm what's going on? could someone please help me on where I went wrong? thank you!
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    6.5 is obtained using radians instead of degrees. In SHM radians are usually used, but I think in the actual exam they will probably specify.
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    (Original post by assassinjeev22)
    hi so I was doing the summary questions for 18.3 and stuck on question 2 ( as follows)

    the displacement of an object oscillating in simple harmonic motion varies with time according to the equation x (mm) = 12cos10t where t = time in seconds after the object was at max positive displacement.

    so for a (i) it said to calculate amplitude which I got as 12mm.
    a (ii) was to find time period which I got as 0.6283185307 a
    question (b) states what will by the displacement of the object when t = 0.1

    I put t = 0.1 in the equation and got 11.99817234 mm

    but the answer at the back says 6.5 mm what's going on? could someone please help me on where I went wrong? thank you!
    cos10t is written in the form: \text{cos}(\omega t)

    where \omega = 2\pi f

    i.e. 360o = 2\pi radians
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    (Original post by assassinjeev22)
    hi so I was doing the summary questions for 18.3 and stuck on question 2 ( as follows)

    the displacement of an object oscillating in simple harmonic motion varies with time according to the equation x (mm) = 12cos10t where t = time in seconds after the object was at max positive displacement.

    so for a (i) it said to calculate amplitude which I got as 12mm.
    a (ii) was to find time period which I got as 0.6283185307 a
    question (b) states what will by the displacement of the object when t = 0.1

    I put t = 0.1 in the equation and got 11.99817234 mm

    but the answer at the back says 6.5 mm what's going on? could someone please help me on where I went wrong? thank you!
    Convention is to work in radians for SHM rather than degrees - this would give 6.48... which rounds off to 6.5mm as required
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    (Original post by Protostar)
    Convention is to work in radians for SHM rather than degrees - this would give 6.48... which rounds off to 6.5mm as required
    Oh my goodness thank you!
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    (Original post by Sint)
    6.5 is obtained using radians instead of degrees. In SHM radians are usually used, but I think in the actual exam they will probably specify.
    Awesome thank you!
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    (Original post by uberteknik)
    cos10t is written in the form: \text{cos}(\omega t)

    where \omega = 2\pi f

    i.e. 360o = 2\pi radians
    Thank you!
 
 
 
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