A thin uniform rod of mass `m` and length `l` is free to rotate about its upper end. When it is at rest, it receives an impulse `J` as its lowest point, normal to its length immediately after impact.
A. `2pisqrt(l//g)`
B. `2pisqrt(2l//3g`
C. `2pisqrt(3l//2g)`
D. `2pisqrt(l//2g)`
