Question

First, you will investigate purely vertical motion. The kinematics equation for vertical motion (ignoring air resistance) is given by
y(t)=y0+v0t−(1/2)gt2,
where y0=0 is the initial position (which is 1.2 m above the ground due to the wheels of the cannon), v0 is the initial speed, and g is the acceleration due to gravity.
Shoot the baseball straight upward (at an angle of 90∘) with an initial speed of 20 m/s.
How long does it take for the baseball to hit the ground?
Express your answer with the appropriate units.

Answer 1

g = 9.81 m/s^2 so g/2 = 4.9

0 = 1.2 + 20 t - 4.9 t^2
or
4.9 t^2 - 20 t - 1.2 = 0
solve quadratic for t (use positive answer choice)

Answer 2

Time = -0.059s and 4.14s
we have to take positive number because time never be negative TIME = 4.14s ( coorect answer in my assignment )