[填空题]
You stand at the top1jeh t3f.- rii4 oe(cvc7 nzmt 7ol0t6g5r 4z/zq8-ytwwo 7ty of a cliff while your friend stands on the ground below you. You drop a ball from rest and see that it takes 1.2 s for the ball to hit the 4/l tz67gmw7 yt7tnootq8w0zr zcy5-ground below. Your friend then picks up the ball and throws it up to you, such that it just comes to rest in your hand. What is the speed with which your friend threw the ball? m/s
