A particle moves with simple harmonic motion in a straight line. In first t sec, after starting from rest,

In the first step it is given the displacement of the particle from the mean position, as a function of the time i.e
x=Acosωt

where, A is amplitude of motion of the particle and ω is its angular velocity.

So, at time t=0, the value of displacement x will be A (as cos0=1)

Hope you understand:)

I got it sir, but the thing is why you took a cosine fuction while there is sine? I mean is there any clue in the question that you should apply cosine to get the correct answer?



And the next is, (when t=t x=A-a) the doubt is at time t the body travelled  distance 'a' but you took it as 'A-a' this step is soo confusing ?