Kinematics: Balloon Speed from Dropped Coin in 4s

[shwvvn]

Homework Statement

A balloon is 30.0 m 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 4.00 s, what is the speed of the balloon?

Homework Equations

v = u + at
s = ut + 1/2 at^2
v^2 = u^2 + 2 as

The Attempt at a Solution

The answer is 12.1 m s^-1.

 

[method_man]

Look here:

https://www.physicsforums.com/showthread.php?t=212504"