Question

If a ball is thrown into the air with a velocity of 42 ft/s, its height (in feet) after t seconds is given by y = 42t − 16t2. Find the velocity when t = 1.

Answer 1

I'm pretty sure its 10

Answer 2

velocity is found using the first derivitive, y'=42-32t 
evaluating this as t=1 gives the velocity after 1 second which is 10ft.