You throw a ball straight up into the air at a speed of 20 m/s. You want to know how high above your hand the ball will be at exactly 2.5 sec after you released it.

a) Of the 5 motion variables - Vi, Vf, a, ΔX, and T, identify which one you are solving for and the magnitudes and directions of all of the others that are known.
b) Which of the motion equations is best to use to determine the height of the ball?
c) How high is the ball above your hand at 2.5 sec after you throw it?

Question

You throw a ball straight up into the air at a speed of 20 m/s.  You want to know how high above your hand the ball will be at exactly 2.5 sec after you released it. 

a) Of the 5 motion variables - Vi, Vf, a, ΔX, and T, identify which one you are solving for and the magnitudes and directions of all of the others that are known. 
b) Which of the motion equations is best to use to determine the height of the ball? 
c) How high is the ball above your hand at 2.5 sec after you throw it?

sophadof · Answer

@Mashy Is this hard for you :/

anonymous · Answer

Nah, the question is just boring :P

anonymous · Answer

Can you tell the answer for a) ?

sophadof · Answer

haha...

sophadof · Answer

I don't know any of this at all! @Mashy

michele_laino · Answer

If I consider the reference system as below:
|dw:1450548678932:dw|
then, the motion of the ball is solved by these ODEs
$$\huge  \left\{ \begin{gathered}
  \ddot z =  - g \hfill \
  \ddot x = 0 \hfill \ 
\end{gathered}  \right.$$

michele_laino · Answer

with the subsequent initial conditions:
$$\huge  \begin{gathered}
  \dot z\left( 0 \right) = {v_z} \hfill \
  \dot x\left( 0 \right) = {v_x} \hfill \
  z\left( 0 \right) = {h_0} \hfill \
  x\left( 0 \right) = 0 \hfill \ 
\end{gathered} $$
|dw:1450548961025:dw|

michele_laino · Answer

we need to know te angle $\theta$ between the velocity, and the positive direction of x-axis:
|dw:1450549085145:dw|