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## Homework Statement

Hi all, I'm trying to understand why my second way of solving this problem doesn't work:

A 3.00kg object is moving in a plane, with its x and y coordinates given by x= 5t^2–1 and y=3t^3 + 2, where x and y are in meters and t is in seconds. Find the magnitude of the net force acting on this object at t = 2.00s

## Homework Equations

xf = xi + vi(t) + (1/2)a(t^2)

## The Attempt at a Solution

I've found the answer with differentiation but I don't think we are supposed to use differentiation in my class so I'm wondering why when I plug the numbers into one of the kinematic equations, I get the wrong answer? I evaluate the object's position at t = 2.00s to be (19 i + 26 j) m and now since I have two components of the objects final position:

19 m = (1/2)ax t^2

26 m = (1/2)ay t^2

to get the acceleration components in order to solve for the Force but this yields the wrong answer. Any clarification is appreciated.