Physics · MOTION IN A STRAIGHT LINE

A driver traveling at \( 54\text{ km h}^{-1} \) applies brakes after a human reaction time \( t_r \), requiring a total stopping distance of \( 30\text{ m} \). When traveling at \( 108\text{ km h}^{-1} \) under identical reaction time and braking deceleration, the total stopping distance becomes \( 90\text{ m} \). Find the reaction time \( t_r \).

1. A
   \( 0.5\text{ s} \)
2. B
   \( 0.8\text{ s} \)
3. C
   \( 1.2\text{ s} \)
4. D
   \( 1.0\text{ s} \)