[填空题]
Francesca, who likes physics experiments,40 kj7qkkp/g8zxq e(h dangles her watch f0rlk9 inv p zc0k7kyn ;+ts/v*rom a thin piece of string while the jetliner she is in takes off from JFK Airport (Fig. 4-58). Shsrc0k9 kit v7*kv +l;0yznpn/e notices that the string makes an angle of 25$^{\circ}$ with respect to the vertical as the aircraft accelerates for takeoff, which takes about 18 s . Estimate the takeoff speed of the aircraft.
