Problem 4
A
If he is staying in the same place km for 1/2 hour, you can assume he's eating lunch or something. He hasn't moved at all, so his speed = distance over time = 0/(0.5) hours = 0
0 = answer
B
Watch out for this. It's a little bit nasty. He starts out at 20 km He ends up at 0 km. It means he is going back to were he started from. If it said velocity, you'd have a problem.
The time taken is 1.5 to 3 hours = 1.5 hours
His speed is d/t
His speed is 20/1.5 = 13.33 km/hr.
Speed = total distance / total time
total time = 3 hours.
Total distance = 40 km which is what the odometer would show.
Speed = 40 km/3 hours = 13.33 km/hour
C
You could just read the graph. He is 10 km from home.