Kinematics: Acceleration and Constant Velocity Phases Steps: - Time to reach 10 m/s: $v = u + at$, with $u = 0$, $v = 10$, $a = 2.5$, so $t = 10 / 2.5 = 4$ s. - Distance during acceleration: $s = ut + \frac{1}{2}at^2 = 0 + \frac{1}{2}(2.5)(4)^2 = 20$ m. - Remaining distance: $100 - 20 = 80$ m at constant 10 m/s. - Time for remaining distance: $t = 80 / 10 = 8$ s; total time $4 + 8 = 12$ s. Why C is correct: - Matches total time from kinematics equations for accelerated motion ($v = at$, $s = \frac{1}{2}at^2$) and constant velocity ($v = d/t$). Why the others are wrong: - A: Underestimates by assuming full distance at constant speed, ignoring acceleration phase. - B: Assumes average speed of 10 m/s over entire race, neglecting initial acceleration time. - D: Overestimates by using lower effective speed or extending …