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It uses C. Kinetic Energy
2.3 seconds
Ignoring air resistance, the flight time is merely a function of gravity and vertical velocity. The vertical velocity will be the initial velocity multiplied by the sine of the angle above the horizon. So:
V = sin(72)*12 m/s
V = 0.951056516 * 12 m/s
V = 11.4126782 m/s
Gravitational acceleration is 9.8 m/s, so divide the vertical velocity by gravitational acceleration to get how long it takes for the ball to reach its apex.
11.4126782 m/s / 9.8 m/s^2 = 1.164559 s
And the old saying "What goes up, must come down" really applies here. And conveniently, it's also symmetric, in that the time it takes to fall will match the time it takes to reach its apex. So multiply the time by 2.
1.164559 s * 2 = 2.329117999 s
Rounding the result to 2 significant figures gives 2.3 seconds.
Hints:
The Earth's energy does not come from eating a balanced diet,
or from ninja turtles, or from getting sleep and exercise.
There are no hamsters running on a treadmill inside the Earth.
God didn't wind up a big spring to operate the Earth.
The Sun provides, and has always provided, almost all of the energy
used on Earth. It was the energy that got stored in dead dinosaurs
to make gas and oil, and it's the energy that makes plants grow, and
gets stored in them so we can get the energy by eating the plants.
