For the first 120 s, displacement = 6 × 120 = 720 m. During the next 6 s, displacement = 6 × 6 + ½ × 1 × 6² = 54 m. Total displacement = 774 m.
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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.
Given u = 28 m s⁻¹, v = 0 and s = 98 m. Using v² = u² + 2as, we get a = −4 m s⁻². Time taken, t = (v − u)/a = 7 s.
Total distance = 200 + 200 = 400 km and total time = 3 + 2 = 5 h. Average speed = 400/5 = 80 km/h. Since displacement is zero, average velocity = 0 km/h.
He travelled 250 m four times: home to shop, shop to home, home to shop and shop to home. Therefore, total distance = 1000 m. Since he returned home, displacement = 0 m.