# Curvilinear Motion: Polar Coordinates (Engineering Dynamics)

1. Jan 31, 2016

### Andy907

1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution
I have stared at this for hours and don't know where to start. I think I need to get r in terms of t but I don't really know how with the information given. I just need a good hint to get started.

2. Jan 31, 2016

### Staff: Mentor

In polar coordinates, what are the equations for the r and θ components of acceleration?

3. Jan 31, 2016

### Andy907

a = (Rdouble dot - Rθdot2)eR + (Rθdouble dot + 2Rdotθdot)eθ

I know a = 15 m/s2. I also know that the dot means the derivative is taken in respect to time. That's where I'm drawing a blank and why I thought the given R equation had to be manipulated in some way to be in terms of t. Or possibly solve for θ in terms of t and then substitute that equation into θ in the original given R equation.

In all the examples we did in class θ was given in terms of t, so it was pretty simple to substitute that equation into the given r equation and then take the derivatives.

4. Jan 31, 2016

### Staff: Mentor

From Eqn. 3.1, in terms of dθ/dt and θ, what is dr/dt?
What is $\frac{d^2r}{dt^2}$ in terms of θ, dθ/dt, and d2θ/dt2.