Please help w/ finding speed of ball 3 secs after launch

[lsniff]

Solve the problem.

A ball is thrown vertically upward from the ground at a velocity of 92 feet per second. Its distance from the ground after t seconds is given by s(t) = 16t^2 + 92t How fast is the ball moving 3 seconds after being thrown?

 

[galactus]

Solve the problem.

A ball is thrown vertically upward from the ground at a velocity of 92 feet per second. Its distance from the ground after t seconds is given by?????? How fast is the ball moving 3 seconds after being thrown?

You ought to preview your post before you hit submit.

 

[lsniff]

changed it

 

[galactus]

Velocity is the derivative of the position function.

 

[DR._Glockman]

First the position function is S(t) = -16t^2+92t, not 16t^2+92t, otherwise the object would never fall back to earth.

V(t) = -32t+92, hence V(3) = -4 ft per second. In other words the object at 3 seconds is falling back to earth at an instantaneous speed of 4 ft per second (when t = 3).