If an arrow on Earth is fired into the air and reaches a hight of 125 m and penetrates the ground where it lands to a depth of 25 cm, what is it's speed when it hits the ground and what is it's deceleration? Of course the acceleration due to gravity is 9.8 m s$\displaystyle ^-2$, but I'm stumped on how to calculate it's final speed. There must be a quck and easy way to do this surely?