# A balloon is rising at 19 m/s when

1. Aug 28, 2008

### imac

1. The problem statement, all variables and given/known data
A balloon is rising at 19 m/s when its passenger throws a ball straight up at 21 m/s. How much later does the passenger catch the ball?

2. Relevant equations
Don't know relevant equations. except v(t)=vot-0.5(9.8)t^2 but I don't think that works.

3. The attempt at a solution
I've attempted this question 4 different ways and times. The answer isn't 4.0816 or 8.1632.

Last edited: Aug 28, 2008
2. Aug 28, 2008

### granpa

v0t? and why is g and 9.8 in the equation?

are you familiar with Galilean relativity?

3. Aug 28, 2008

### imac

Fixed it sorry, no... I'm not familiar with Galilean relativity.

4. Aug 28, 2008

### granpa

velocity=initial velocity + acceleration * time
Galilean invariance or Galilean relativity is a principle of relativity which states that the fundamental laws of physics are the same in all inertial frames. Galileo Galilei first described this principle in 1632 in his Dialogue Concerning the Two Chief World Systems using the example of a ship traveling at constant speed, without rocking, on a smooth sea; any observer doing experiments below the deck would not be able to tell whether the ship was moving or stationary. Today one can make the same observations while travelling in an aeroplane with constant velocity. The fact that the earth on which we stand orbits around the sun at approximately 30 km/s offers a somewhat more dramatic example.