To solve the problem, you should first convert the 20ft to meters so it is much easier.
20 feet is equals to 6 meters; rounded off to the nearest whole number.
Solution:
V1 = v
V2 = 0
T1 = ½ mv^2
T2 – 0
U 1-2 = -mgh
d = 6m
--AB^2 = (10m)^2 = d^2 + y^2 = (6m)^2 = y^2
Y^2 = 100 – 36 = 64
Y = sqrt64
h = 10 – y = 10 – sqrt64 = 10 – 8 = 2 m
U 1- 2 = -m (9.81) (2) = -19.62
T1 + U1-2 = T2
1/2mv^2 – 19.62m = 0
v^2 = (2) (19.62) = 39.24