What are the magnitude Δ v and angle θ of the change in velocity if the initial velocity is 50.0 m/s south and the final velocity is 35.0 m/s west? Let the angle θ be measured relative to the east direction (e.g., θ = 90 ∘ means Δ → v points north, θ = 180 ∘ means Δ → v points west, etc.).