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The movement of an object is described by the velocity function:

$${\bf v}(t)=(t+1){\bf i}+t^4 {\bf j}+ {\bf k}$$

What is the speed of this object when its velocity is the vector $\langle 4,81,1 \rangle$?

$4{\bf i}+81{\bf j}$

${\bf i}+108{\bf j}$

${\bf i}+108{\bf j}+{\bf k}$

$81{\bf j}$

$4{\bf i}+81{\bf j}+{\bf k}$