Final answer:
The relative velocity between the car and the truck is 10 km/hr east.
Step-by-step explanation:
The velocity of the car with respect to Earth is 80 km/hr east. The velocity of the truck with respect to Earth is 70 km/hr south. To find the relative velocity between them, we can use the velocity addition rule.
The relative motion equation is given by:
Relative velocity = Velocity of car with respect to Earth + Velocity of truck with respect to Earth
Substituting the given values:
Relative velocity = 80 km/hr east + (-70 km/hr) south
Simplifying, we get:
Relative velocity = 10 km/hr east