[填空题]
Francesca, who likes pa ex4t m:*wq 9wpz 5yh6a7oc+mhysics-1/ukuaqs 6 hvswn2q. experiments, dangles her watch from a thin piece of string while the jetliner she is in takes off .a6 hqq/s vw-u 2ksu1nfrom JFK Airport (Fig. 4-58). She 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.
