Answer:
C.The car appears to be moving 30 km/hr in the opposite direction of the bus.
Explanation:
There are two reference systems involved in this situation:
- Reference system S: this is the reference system where velocities are measured with respect to the ground. In this reference system, the car is parked, so its velocity is
- Reference system S': this is the reference system moving with the bus. This reference system is moving with a velocity of with respect to the reference system S
Calling the velocity of the car in the reference system S', we have:
From which
and the negative sign means that a passanger in the bus observes the car moving in the opposite direction.