Relative Motion: Example

1. Nathan is walking north at 2 ms-1 and is being followed by Leah who is walking north at 3 ms-1. What is the velocity of
(i) Nathan relative to Leah?
(ii) Leah relative to Nathan?

2. Sam is walking east at 5 km/h towards Ken who is walking west at 4 km/h. What is the velocity of
(i) Sam relative to Ken?
(ii) Ken relative to Sam?

3. Sam and Ken passed each other and Sam is now walking east away from Ken who is walking west at 4 km/h. What is the velocity of
(i) Sam relative to Ken?
(ii) Ken relative to Sam?

4. Nathan and Leah were aboard a train that was travelling south at 15 ms-1. Nathan walked from the front carriage to the back carriage at an average speed of 4 ms-1 relative to the train while Leah walked from the back carriage to the front carriage at an average speed of 3 ms-1 relative to the train. What was
(i) Nathan's velocity relative to the ground?
(ii) Leah's velocity relative to the ground?
(iii) Leah's velocity relative to Nathan?
(iv) Nathan's velocity relative to Leah?

5. Chris is walking along a moving footway at 3 km/h west relative to Leah who is stationary on the footway. Leah is moving west at 5 km/h relative to a Nathan who is standing still on the path next to the footway. Sam is walking east towards Nathan along the path next to the footway. What is the velocity of
(i) Chris relative to Nathan?
(ii) Sam relative to Leah?
(iii) Sam relative to Chris?
(iv) Chris relative to Sam?

Answers: Relative Motion

1. Nathan is walking north at 2 ms-1 and is being followed by Leah who is walking north at 3 ms-1. What is the velocity of
(i) Nathan relative to Leah?
1 ms-1 south

(ii) Leah relative to Nathan?
1 ms-1 north

2. Sam is walking east at 5 km/h towards Ken who is walking west at 4 km/h. What is the velocity of
(i) Sam relative to Ken?
9 km/h east
(ii) Ken relative to Sam?
9 km/h west

3. Sam and Ken passed each other and Sam is now walking east away from Ken who is walking west at 4 km/h. What is the velocity of
(i) Sam relative to Ken?
9 km/h east

(ii) Ken relative to Sam?
9 km/h west

4. Nathan and Leah were aboard a train that was travelling south at 15 ms-1. Nathan walked from the front carriage to the back carriage at an average speed of 4 ms-1 relative to the train while Leah walked from the back carriage to the front carriage at an average speed of 3 ms-1 relative to the train. What was
(i) Nathan's velocity relative to the ground?
11 ms-1 south

(ii) Leah's velocity relative to the ground?
18 ms-1 south

(iii) Leah's velocity relative to Nathan?
7 ms-1 south

(iv) Nathan's velocity relative to Leah?
7 ms-1 north

5. Chris is walking along a moving footway at 3 km/h west relative to Leah who is stationary on the footway. Leah is moving west at 5 km/h relative to a Nathan who is standing still on the path next to the footway. Sam is walking east towards Nathan with a speed of 4 km/h along the path next to the footway. What is the velocity of
(i) Chris relative to Nathan?
8 km/h west

(ii) Sam relative to Leah?
9 km/h east

(iii) Sam relative to Chris?
12 km/h east

(iv) Chris relative to Sam?
12 km/h west