Elevator Problem

To find the final velocity, $v_f$, of an object undergoing constant acceleration, we use the kinematic equation:

$v_f = v_i + a \cdot t$

where $v_i$ is the initial velocity, $a$ is the acceleration, and $t$ is the time elapsed.

From the problem statement, we have: The elevator starts at the ground floor, which means its initial velocity is $v_i = 0\,\mathrm{m/s}$. The acceleration is $a = 2.8\,\mathrm{m/s^2}$. The time is $t = 3\,\mathrm{s}$.

Substitute these values into the equation:

$v_f = 0 + (2.8) \cdot (3)$

$v_f = 8.4\,\mathrm{m/s}$

The elevator's velocity after 3 seconds is $8.4\,\mathrm{m/s}$.