v1 = 5 kmh-1, v2 = 7.5 kmh-1, d = 2.5 km
Time for the man to reach the market
= t1 = d/v1= 2.5/5 = 0.5 h = 30 min
Time for the man to return from the market
= t2 = d/v2 = 2.5/7.5 = 1/3 h= 20 min
1. To find the average velocity,
Average velocity = Total path length/Total time taken
(a) During the interval between 0 to 30 min,
Displacement = 2.5 km
time = 30 minutes
∴ Average velocity = 2.5 km/30 min = 5 kmh-1
(b) interval between 0 and 50 minutes,
Displacement = 0
∴ Average velocity = 0
(c) During between 0 to 40 minutes,
Displacement = 2.5 km – 7.5 kmh-1 × 10 min = 1.25 km
time = 40 minutes
∴ Average velocity = 1.25/40 min = 1.875 kmh-1
2. To find the average speed:
Average speed = Total path length/Total time taken
(a) During the interval between 0 to 30 min
Path length = 2.5 km
time = 30 minutes
∴ Average speed = 2.5 km/30 min = 5 kmh-1
(b) During the interval between 0 and 50 minutes,
Path length = 2.5 km + 2.5 km
Time taken = 50 minutes
∴ Average speed = (2.5 km + 2.5 km)/50 min = 6 kmh-1
(c) During 0 to 40 minutes
Path length = 5 kmh-1 × 30 min + 7.5 kmh-1 × 10 min
2.5 km + 1.25 km = 3.75 km
time = 40 minutes
∴ Average velocity = 3.75 km/40 min = 5.625 kmh-1