Velocity: \( v_1 = 20 - 10 t \), \( v_2 = 30 - 10 t \).
Set \( v_1 = v_2 \): \( 20 - 10 t = 30 - 10 t \), not possible directly, so consider relative motion or
when one overtakes.
Correction: They have same velocity magnitude when one is going up and other down. Time to max height: \(
t_1 = 2 \, \text{s} \), \( t_2 = 3 \, \text{s} \).
After \( t_2 \), \( v_2 = 30 - 10 (t - 3) \) downward. At \( t = 5 \, \text{s} \): \( v_1 = 20 - 10 \cdot
5
= -30 \, \text{m/s} \), \( v_2 = 30 - 10 \cdot 2 = 10 \, \text{m/s} \) (no match).
Instead, equal velocity occurs at \( t = 1 \, \text{s} \) relative difference: \( v_1 = 10 \, \text{m/s}
\), \( v_2 = 20 \, \text{m/s} \) (misstep). Correct: Equal magnitude opposite direction after \( t = 2 \,
\text{s} \), \( v_2 = 10 \, \text{m/s} \) down at \( t = 4 \, \text{s} \), \( v_1 = -20 \, \text{m/s} \).
Time = \( 4 \, \text{s} \).