A car is at an initial velocity of 100km/h [north] and has a constant acceleration of 4m/s^2 [south]. After 6 seconds what is its final velocity?

Use this kinematics equation:

Vf = Vi + aΔt

Vf is the final velocity, Vi is the initial velocity, a is the acceleration, and Δt is the elapsed time.

Assign northward velocity/acceleration as positive and southward as negative. Given values:

Vi = 100km/h = 27.8m/s

a = - 4m/s²

Δt = 6s

Plug in the values and solve for Vf:

Vf = 27.8 - 4 (6)

Vf = 3.8m/s north