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# The motion of a particle is described by equation $x= a+bt^2$ where $a=15\;cm,b=3\;cm/s$ The instantaneous velocity at time 3 will be

$\begin{array}{1 1} (a) \;36\;cm/s \\ (b) \;18\;cm/s\\ (c) \;16\;cm/s\\ (d) \;32\;cm/s\end{array}$

$x=a+bt^2$
$a= 75\;cm/s$
$b= 3\;cm/s^2$
Velocity $=V=\large\frac{dx}{dt}$$=2bt$
at $v=2 \times 3 \times 3$
$\qquad= 15\;cm/s$