Chapter 11.8, Problem 2P

Suppose that a car with a door open at right angles $\left(\theta ={90}^{°}\right)$ starts up and accelerates at a constant rate $a=1\text{mph}/\text{sec}.$ The differential equation for $\theta (t)$ is $\stackrel{\to }{\theta }=-A\sin \theta$ where $A=3a/2w$ for a uniform door of width $w .$ If $w=3.5\text{ft},$ find how long it takes for the door to close.