Answer:
21.1 m/s
Explanation:
The motion of the stone is a uniformly accelerated motion (free fall), so we can find the final velocity of the stone by using the following suvat equation
[tex]v^2-u^2=2as[/tex]
where
v is the final velocity
u is the initial velocity
a is the acceleration
s is the vertical displacement
For the stone in this problem, taking upward as positive direction, we have:
u = +7.19 m/s is the initial velocity
[tex]a=g=-9.8 m/s^2[/tex] is the acceleration of gravity
s = -20.1 m is the displacement
Solving for v, we find the final velocity:
[tex]v=\sqrt{u^2+2as}=\sqrt{(7.19)^2+2(-9.8)(-20.1)}=\pm 21.1 m/s[/tex]
And the correct solution is the one with negative sign, since the final velocity is downward:
[tex]v=-21.1 m/s[/tex]
Therefore, the final speed (the magnitude of the velocity) is
[tex]v=21.1 m/s[/tex]
