# Question #a91b2

##### 1 Answer

Oct 17, 2016

A ball is thrown upward in the air, and its height above the ground after t seconds is

Differentiating w.r.to t we get the upward velocity

So

when the ball will be traveling downward at 41.5 feet per second,then

Inserting this value in (1) we get

So the ball will be traveling downward at 41.5 feet per second after 3.89s of its projection upward from the ground.