Answer:
magnitude of A − B = 15.81 km
Explanation:
Vector A points in the negative y-direction and has a magnitude of 5 km. Vector B points in the positive x-direction and has a magnitude of 15 km.
According to Cartesian coordinate system, the resultant will start either from tail of A and ends at head of B and vice-versa.
A(0,-5)
B(15,0)
A - B = (-15 i - 5 j )
Magnitude of the vector is given by
|A - B| = 
|A - B| = 
|A - B| = 15.81 km
Over time, yes. It will over time gain more momentum
The acceleration of the car is solved by subtracting the initial speed from the final speed then dividing the result by the elapsed time.
initial speed = 72 km/hr = 20 m/s
final speed = 0 m/s
elapsed time = 5 seconds
acceleration = (0 m/s – 20 m/s) / 5 s
acceleration = - 20m/s / 5 s
acceleration = -4 m/s^2