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Mechanical Properties Of Fluids

Question
CBSEENPH11020204

Figures 14.29 correspond to two circular motions. The radius of the circle, the period of revolution, the initial position, and the sense of revolution (i.e. clockwise or anti-clockwise) are indicated on each figure. 
Obtain the corresponding simple harmonic motions of the x-projection of the radius vector of the revolving particle P, in each case.


Solution
Time period, t = 2 s 
Amplitude, A = 3 cm
At time, t = 0, the radius vector OP makes an angle π/2 with the positive x-axis. 
i.e., phase angle Φ = +π/2 
Therefore, the equation of simple harmonic motion for the x-projection of OP, at the time t, is given by the displacement equation

straight x space equals space straight A space cos space open square brackets fraction numerator 2 πt over denominator straight T end fraction plus straight ϕ close square brackets space

space space equals space 3 space cos space open parentheses fraction numerator 2 πt over denominator 2 end fraction plus straight pi over 2 close parentheses

space space equals space minus space 3 space sin space open parentheses fraction numerator 2 πt over denominator 2 end fraction close parentheses space

space space equals space minus space 3 space sin space straight pi space straight t space c m 
b) Time Period, t = 4 s 
Amplitude, a = 2 m 
At time t = 0, OP makes an angle π with the x-axis, in the anticlockwise direction.
Hence, phase angle Φ = +π 
Therefore, the equation of simple harmonic motion for the x-projection of OP, at the time t, is given by, 
straight x space equals space straight a space cos space open square brackets fraction numerator 2 πt over denominator straight T end fraction space plus space straight phi close square brackets space

space space space equals space 2 space cos space open parentheses fraction numerator 2 πt over denominator 4 end fraction space plus space straight pi close parentheses

therefore space straight x space equals space minus 2 space cos space open parentheses straight pi over 2 straight t close parentheses straight m