The ball is dropped from rest, so its velocity at time [tex]t[/tex] is
[tex]v=at[/tex]
where [tex]a=-g[/tex] is the acceleration due to gravity. After 7 seconds, we have
[tex]v=\left(-9.8\,\dfrac{\mathrm m}{\mathrm s^2}\right)(7\,\mathrm s)[/tex]
[tex]\implies v=68.6\,\dfrac{\mathrm m}{\mathrm s}[/tex]
so the answer is B.
