a balloon is 30m above the ground and is rising vertically with a uniform speed when a coin is dropped from it. if the coin reaches the ground in 4 seconds, what is the speed of the balloon?
The height h of the coin is
h(t) = 30 + vt - 4.9t^2
so, solve for v when h(4) = 0
30 + 4v - 4.9*4^2 = 0
v = 12.1 m/s