A ball is dropped from a height of 61 feet. Its height above ground (in feet) t seconds later is given by s(t)=16t2+61\displaystyle {s}{\left({t}\right)}=-{16}{t}^{{2}}+{61}.
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  1. At what time does the ball hit the ground?
     
  2. What is the instantaneous velocity of the ball when it hits the ground?
     
  3. What is the average velocity during its fall?