Calculate the magnitude of particle acceleration

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To calculate the magnitude of particle acceleration, the position vector is given as r=42t^2i + 41t^3j + 6k. The acceleration is derived from the second derivative of the position vector, resulting in the components 246j and 84i. At t = 15 seconds, substituting this value yields an acceleration vector of 3691. The confusion arose from incorrectly simplifying the acceleration components. The correct approach involves maintaining the vector format throughout the calculations.
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Homework Statement



A particles position is given by r=42t^2i + 41t^3j + 6k. Calculate the magnitude of its acceleration at time t = 15 seconds

Homework Equations





The Attempt at a Solution



to find the acceleration i found the second derivative which i had as 246t + 84. Then i put 15 in as t and got 3774, but according to the answers i should get 3691. What did i do wrong
 
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You are dealing with vectors. The acceleration is 246tj + 84i, not just 246t + 84.
 
but do i still have to find the second derivative using this? Can you give me a hint on how to do this?
 
ive worked this one out. Thanks for the hint
 

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