Simple harmonic motion of a pendulum: find angle and velocity at 1.6 s

[FChebli]

Homework Statement

:[/B]

BoB released from rest, L = 102 cm, theta = +-5 degrees, g = 9.81 m/s2
assume a SHM
(I) Determine the angle theta after 1.6 s
(II) Determine the magnitudes of velocity & acceleration of the BoB at 1.6 s

Homework Equations

theta = A sin (w t + phai)

The Attempt at a Solution

Does phai represent the period? And how do I get it?
Do I derive theta once & twice? And why?
How do I get w & A?

Thank you!

 

[tiny-tim]

Welcome to PF!

Hi FChebli! Welcome to PF!

(have a theta: θ and a phi: φ and an omega: ω )

θ = A sin(ωt + φ)

A is the maximum value (θ varies between ±A), which you can find from the question

ω is the frequency … to find the period, you need the value of t which makes (ωt + φ) increase by 2π

φ is the phase … it's often zero, but not always … you find it by putting t = 0, and seeing what θ is (or dθ/dt, if that's given instead)

 

[FChebli]

Thank you so much! :)