Assuming no air restance the speed when the ball comes back to the starting point will be again 8ms but directed DOWNWARDS; we can express this by saying that it will equal to −8ms adding a minus to indicate the downward direction.
To find the time of flight we use:
vf=vi+at
Where:
a is the acceleration of gravity (downwards, −9.8ms2);
vi=+8ms
vf=−8ms
So, we get:
−8=8−9.8t
−16=−9.8t
t=169.8≈1.6s
The answer is "B"
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