Solve: d^2x//dt^2 + g sin theta t =0 if theta=g//l , and g and l are constants?

2 Answers
Apr 27, 2018

x(t) = - g sin(g/1) t^2/2 + At + B

Explanation:

You are asking for the solution to:

(d^2x)/(dt^2) = - g sin(g/1)

implies (d x)/(dt) = - g sin(g/1) t + A

implies x(t) = - g sin(g/1) t^2/2 + At + B

Apr 28, 2018

x = l^2/g \ sin theta t + At + B

Explanation:

We have:

(d^2x)/(dt^2) + g sintheta t = 0 where theta=g/l, a constant

Which we can write as:

(d^2x)/(dt^2) = - g sintheta t

We can "separate the variables" , to get:

(dx)/(dt) = int \ - g sintheta t \ dt

And integrating give us:

(dx)/(dt) = g/theta cos theta t + A

And repeating we get:

x = int \ g/theta cos theta t + A \ dt

So that:

x = g/theta^2 sin theta t + At + B

\ \ = g/(g/l)^2 sin theta t + At + B

\ \ = g l^2/g^2 \ sin theta t + At + B

\ \ = l^2/g \ sin theta t + At + B