Object Thrown Vertically Upward

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A ball is thrown vertically upward at 20.0 m/s, and the discussion focuses on calculating its speed at 16 m and the time taken to reach that height. The only force acting on the ball is gravity, as it is in free flight. The equations of motion are derived using acceleration due to gravity (a=g), with relevant formulas for velocity and displacement provided. The mention of two answers relates to the ball's ascent and descent phases, where it reaches the same height twice. Understanding these concepts is crucial for solving the problem effectively.
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1. Homework Statement :

A ball is thrown vertically upward with a speed of 20.0m/s.

i) How fast is it moving when it reaches 16m
ii) How long is required to reach this height?
iii) Explain why there are two answers.
2. The attempt at a solution
I assume there are two vectors. The force of the ball going upwards and the force of gravity pulling the ball downwards.


Thanks in advance for helping.
 
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There is no force upwards because the ball is in free flight. Therefore the only force is due to gravity.

Using a=g you can derive all the formula you need by integrating wrt time:

a=g
v=v0+g*t
d=v0t+(1/2)*g*t^2
 

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