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**1. Homework Statement**

Suppose that the position function of a spaceship is r(t) = (3+t)i + (2+ln T)j + (7-4/t^2+1)k. Suppose you want the ship to coast to a space station located at (6.4.9). What time should you turn your engine off?

**2. Homework Equations**

r' = velocity. r" = acceleration.

**3. The Attempt at a Solution**

I guess when you turn the engine off there is no acceleration. So

|r"| = |<0,-1/t^2,(8(t^2+1)-16t^2(t^2+1)^4)/(t^2+1)^4| = 0. But I'm not really sure what to do after that or if this is even the right approach. Any suggestions? Thanks!!