The bus, initially moving at a speed of 54 km / h, starts to move 75 m in front of a traffic light and stops

The bus, initially moving at a speed of 54 km / h, starts to move 75 m in front of a traffic light and stops right next to it. Find the braking time, the acceleration of the bus and the speed of the bus 3s after the start of braking.

Problem data: V1 (initial bus speed) = 54 km / h (in SI V1 = 15 m / s); S1 (full stopping distance to traffic lights) = 75 m; t1 (considered braking time) = 3 s.

1) Acceleration of a given bus during braking (slow motion): a = (V2 ^ 2 -V1 ^ 2) / 2S = -152 / (2 * 75) = -1.5 m / s2.

2) Total braking time: t = -V1 / a = -15 / (-1.5) = 10 s.

3) The speed of the given bus after 3 seconds: V2 (3) = V1 + a * t1 = 15 – 1.5 * 3 = 15 – 4.5 = 10.5 m / s2.