Terminal Velocity: Calculate Mass of 22cm Ball

[StephenDoty]

v^2= (4mg)/A

so if a 22cm diameter ball has a terminal velocity of 85m/s, what would the mass of the ball be?
A = 4pi r^2
22cm= 0.22m
v^2 = (39.2m)/(4pi (.11)^2)
7225= (39.2m)/(pi*.0484)
So I got 28kg for the mass and that is not right. Please help.

Stephen Doty

 

[PhanthomJay]

You have incorrectly noted that A=4pi r^2, where of course you meant A= pi r^2.

 

[StephenDoty]

I know the area of a circle is pi r^2
but isn't the area of a sphere or a ball 4pi r^2 ?

 

[kamerling]

In problems with air resistance we use area of the largest cross section of an object with a plane that is perpendicular to its direction of movement. In this case that is a circle with radius r