Solutions

1. A car travels from A to B as shown on the map below. The distance from A –B is 50km and the car starts off at an average speed of 50kmhr-1 hoping to make the journey in 1 hour. After 20km the car has to stop at some road works for 10 minutes, calculate the average speed be for the rest of the journey so that the car arrives on time?

Hint:

  • Calculate how long it takes to get from A to B using v=s/t
  • Add the time waiting then subtract from 1 hour to give the time remaining
  • calculate the average speed for the rest of the journey from v=d/t

Solution:

2. Two identical boats that can travel 5ms-1 in still water have a race in a river that is flowing at 2ms-1. Boat 1 travels 100m from A to B and back and boat 2 travels100m from A to C and back. Who wins and by how many seconds?

Hint:

  • Boat 2 has a velocity 5-2 to C and 5+2 on the way back
  • For boat 1 to travel directly to B it must be heading up river with a velocity of 2ms-1

Solution:

You can see how the boat in this video is pointing upstream all the time as it crosses the river

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