[单选题]
A roller coaster starts at a dmq0o:k fi cq0i,s7d4 point c( njty 8caza 8t,z+3j30 m above the bottom of a dip with a speed of 25 m/s (See Fig. 6-2). Neglect j8actz(j ,c8t az y+3nfriction, what will be the speed of the roller coaster at the top of the next slope, which is 45 m above the bottom of the dip?
