the ball is shot straight up at twice its terminal speed. What is its initial acceleration?
The ball is shot straight down at twice its terminal speed. What is its initial acceleration?
1 Answer

At terminal speed,
F(air drag at terminal) = pull of gravity = mg
F(air drag at twice terminal speed) = 4*F(air drag at terminal speed) because air drag goes up with square of speed.
So, F(air drag at twice terminal speed) = 4mg.
When shot up wards, there is a drag of 4mg downward from air resistance, and 1mg from gravity, so total acceleration = 5g downward.
When shot downwards, total force is 4mpg upward and 1mg downward, so total acceleration = 3g upward.