If a ball is thrown into the air with a velocity of 39 ft/s, its height (in feet) after t seconds is given by y = 39t − 16t2. find the velocity when t = 1.

For this case we have the following equation:
 y = 39t - 16t2
 Deriving we have that the speed is given by:
 v = 39 - 32t
 Evaluating the speed for t = 1 we have:
 v = 39 - 32 (1)
 v = 39 - 32
 v = 7 feet / s
 
 the velocity when t = 1 is:
 v = 7 feet / s

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