Verified answer

Answer:

a. 2 seconds

Step-by-step explanation:

Given :

• h(t) = 64t - 16t²
• dh/dt = 64t - 16t²

Solution :

Where h is the height in feet and t is the time in secs. So, The ball hit the ground if h = 0,

• h = - 16t² + 64t = 0
• h = -32t + 64t = 0
• 32t = 64t
• t = 64/32
• t = 2

Hence, The ball hit the ground at a time of 2 seconds.