136. The velocity of a body is given by the equation $v=6 t^{2}+1$. Find the equation of motion, if in the time $t=3$ s the body has traveled a distance $s=60 \mathrm{M}$.
Solution. $1^{0}$. We have $d s=v d t=\left(6 t^{2}+1\right) d t$; then $s=\int\left(6 t^{2}+1\right) d t=$ $=2 t^{3}+t+C$.

$2^{0^{\circ}}$. Substituting the initial conditions $s=60 \mathrm{M}$, $t=3 \mathrm{c}$ into the found equation, we get $60=2 \cdot 3^{3}+3+C$, from which $C=3$.

$3^{\circ}$. The desired equation will take the form $s=2 t^{3}+t+3$.