Answer:
2.04 seconds.
Explanation:
We use an equation of motion of a body acting under gravity:
v = u + gt where u = initial velocity, g = acceleration due to gravity (9.81 m /s^-2) , v = final velocity and t = the time in seconds.
At the top of the upward journey v = 0 so we have:
0 = 20 - 9.81t (the g is negative because the gravity acts downwards).
9.81t = 20
t = 20/9.81
= 2.04 seconds.
