Question

An iron robot falls from rest at a great height. neglecting air resistance, what is its speed after it has fallen for 3.5 seconds? 13.3 m/s 9.8 m/s 34.3 m/s 9.8 m/s2

Answer 1

In an uniformly accelerated motion, the velocity of the object follows the law:
$v(t) = v_0 + at$
where $v_0$ is the initial velocity, a the acceleration and t the time.

In our problem, the robot starts from rest, so the initial speed is zero: $v_i =0$. The robot is in free fall, so the acceleraion is the gravitational acceleration $g=9.81 m/s^2$. therefore, after a time $t=3.5 s$, the velocity is 
$v(3.5 s)= 0 + (9.81 m/s^2)(3.5 s)=34.3 m/s$