I can't reliably get the mass to be launched at the speed i want.
When i key v = -1.11E4 and click play, it doesnt even go halfway. Nothing happens if i continue to change the velocity value.


But i found i was able to make it work again if i always "reset" it by selecting "random spot" then return back to "Earth surface". However, the value of -1.11E4 never works. In fact, -1.15E5 will also cause it to return back to Earth surface. Only value of -1.16E4 onwards will it reliably reach the moon.
made the menu bar remember but the first time need to set manually
theory says 11200 m/s, to reach infinity as speed 0
but in practice it could be larger like 11500 m/s, say to reach a very far place with a speed of 100 to 1000 m/s
i have change the launch position to be slightly above sea level surface of Earth .
i think it works for 11400 m/s now.
http://en.wikipedia.org/wiki/Escape_velocity also say it is roughly 11200 m/s, so it should be  larger  than 11200 m/s according to the computer model about 11500 m/s should escape


1. I wonder if there's anything wrong in the applet calculation values (rounding off issues) that causes the value to be different from that calculated in the worksheet.
i checked, the values i used are pretty accurate, it is the theory that is problematic.
error analysis
(11500-11200)/11200 = 2.7 % error is it acceptable?[/b][/color]

2. Can it be done such that i need not do the "manual reset" each time i want to test a new velocity?
done, the menu remember past last values, but need to set it for first time.[/b][/color]