Answer:
A. 15m/s
Explanation:
Since air resistant is neglected, gravity is the only force affecting the rock. Suppose the constant gravitational acceleration g = -10 m/s2, negative because it's in the opposite direction (downward) to the upward velocity. We can calculate the velocity of the rock after 2 seconds using the following equation of motion:
[tex] v = v_0 + \Delta t g[/tex]
where v0 = 5 m/s is the initial velocity, t = 2 seconds
[tex] v = 5 - 2*10 = 5 - 20 = -15m/s[/tex]
So the rock speed after 2 seconds is 15 m/s
