Two Dimensional Motion and Vectors, Page 14

Solved Examples of Relative Velocity

1. Truck A moves at a speed of 20 m/s toward east and another truck B moves that with the speed of 10 m/s toward west. What is the velocity B with respect to the velocity A? 
   
   Solution: 
   
   Given: . 
   
   A velocity vector pointing east is positive and a velocity vector pointing west is negative, so . 
   
   Thus,
   
   
   
   
   
   The magnitude of the velocity of B with respect to A is 30 m/s and the direction west is indicated with the negative sign in the solution. 
2. A boy rides a bicycle with a velocity of 3 m/s on a rainy day and rain falls down with a velocity of 4 m/s. Which direction should the boy hold the umbrella to protect himself from the rain? 
   
   Solution: 
   
   Given: 
   
   
   
   
   The boy has to hold the umbrella 53° away from the horizontal position.