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## Homework Statement

An object has a position given by r-> = [2.0 m + (1.00 m/s)t] i + [3.0m−(5.00 m/s2)t2] j, where all quantities are in SI units. What is the magnitude of the acceleration of the object at time t = 2.00 s?

## Homework Equations

All I am thinking here is that I can find acceleration by deriving velocity from the position vector, then taking the deriving the velocity vector.

## The Attempt at a Solution

deriving the original r vector for velocity gave me V=[2.0m + (1.00 m/s)(1)]i + [3.0m - (5.00 m/s^2)(2t)]j

deriving the velocity vector for a gave me A=[2.0m + (1.00 m/s)]i + [3.0m - (5.00 m/s^2)(t)]j

once I have this vector for acceleration, I get the acceleration at t=2.00s to be A(2.00s)=(3m)i + (-7m/s^2)j.

I find the vector A=7.616 m/s^2, which my online software says is incorrect. Can I get some input here?