Question

A Dodge Stealth is driving at 57 mph on a highway. It passes a BMW going the same direction. The BMW is moving 11 mph backward relative the Dodge. What is the velocity of the BMW? Let the positive direction be forward. (Show all work)

Answer 1

The speed of the BMW with respect to an inertial reference system is:

$V_t = V_m + V_{rm}$

Where

$V_t$ = speed with respect to the inertial reference system (road)

$V_m$ = Speed of the mobile reference system with respect to the inertial system.

$V_{rm}$ = Speed of the object in relation to the mobile reference system.

$V_t$ =?

$V_m$ = 57 mph

$V_{rm}$ = -11 mph

$V_t = 57 + (-11)$

$V_t = 46$ mph

The speed of the BMW is 46 mph