For constant velocity, the area from 20–100 s is a rectangle: 3 × 80 = 240 m. For decreasing velocity, area from 100–120 s = ½(3+2)×20 = 50 m. Total displacement = 320 m; average acceleration = (2−0)/120 = 0.0167 ...
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An object kept on the Earth can be considered at rest relative to the Earth, because its position does not change with respect to the Earth. However, relative to the Sun, it is moving.
The bus speed is 10 m s⁻¹. During reaction, it travels 5 m. Braking distance = 10²/(2 × 2.5) = 20 m. Total stopping distance = 25 m, less than 30 m. Yes, it stops safely.
During acceleration, distance = ½ × 5 × 20 = 50 m. At constant speed, distance = 20 × 10 = 200 m. During braking, distance = ½ × 6 × 20 = 60 m. Total distance = 310 m.
Initial speed u = 54 km h⁻¹, final speed v = 36 km h⁻¹, and time = 36 s = 0.01 h. Average speed = 45 km h⁻¹. Distance = 45 × 0.01 = 0.45 km = 450 m.