Upgrade to access all content for this subject

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?

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

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

$5$

$\sqrt{65}$

$\sqrt{11}$