Can Initial Speeds of 0m/s Solve This Kinematics Problem?

[Ukitake Jyuushirou]

i need some help please

1) A spelunker drops a stone from rest into a hole. The speed of sound in air is 343m/s and the sound of the stone striking the bottom is heard 1.5s after the stone is dropped. How deep is the hole?

none of my answers come close to the book's ans of 10.6 :(

2) The Earth moves around the sun in a circular orbit of radius 1.4e11. The time taken for 3 months orbit is 7.89e6, what is the magnitude of the average velocity of the Earth during this period?

i have found the circumference, and then the value of the circumference is divided by 12 and then multiplied by 3 to give 3 months distance. then it is divided by the time taken which gives me 2.99e4 but the ans in the book says the ans is 2.69e4 :(

An eagle is flying horizontally at 6m/s with a fish in its claws, it accidentally drops the fish a) how much time passes before the fish speed doubles? b) how much time is needed for the fish speed to double again?

 

[arunbg]

Remember that velocity is a vector, and average acceleration is given by
a=\frac{|\Delta\vec{v}|}{\Delta t}

Arun