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Multivariable Calculus

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Speed at a Given Time

MVCALC-S2TLYZ

The movement of an object in the $xy$-plane is described by the position function:

$${\bf r}(t)=(3t+1){\bf i} + t^2 {\bf j}$$

...where time is measured in seconds.

What is the speed of this object two seconds after it starts moving?

A

$7{\bf i} +4{\bf j}$

B

$3{\bf i} +4{\bf j}$

C

$5$

D

$\sqrt{65}$

E

$\sqrt{11}$