Problem #1 (3+1+1=5 points) First stone is dropped (released from rest) from a top of a cliff. A second stone is thrown directly downwards from the same cliff 0.6 s later. The cliff is 15 m above the ground, Find: (a) total time of flight (in sec) of the first stone before it hits the ground (1 point); (b) the initial speed of the second stone (in m/s) if both stones are to hit the ground at the same time (1 point).