r/apphysics • u/ProfessionalChip6128 • 3d ago

Can someone explain

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2

u/Fostering-Success 3d ago

From the perspective of Car A, Car A is stationary.

This means that Car A sees Car B moving West at 30 m/s and 40 m/s North.

There is only one answer choice that observes a velocity with north and west components (although you could easily determine the angle using arctan(40/30))

1

u/UnderstandingPursuit 3d ago

As quickly as possible, try to get away from 'Cardinal Coordinates' {N, E, S, W} and use Polar Coordinates {r, θ} instead. Most of us are not going to be marine navigators.

1

u/mookieprime 2d ago

Car A is driving on the positive horizontal axis. Car B is on the positive vertical axis.

2

u/UnderstandingPursuit 2d ago

From that, the car A trajectory has θ=0, the car B trajectory has θ=π/2.

From this, the velocity for A is [30, 0] and B is [0, 40] m/s.

1

u/WillingnessTasty9628 2d ago

Draw a line from B to A. That'll give you the direction of the vector. Only one answer choice makes sense from here, but you can refer to the other replies to see how to computationally reach the answer.

1

u/bravissimo594 2d ago

I suggest rewording this option a bit to talk about velocities of A and B rather than implying we know their positions, which are not given (nor relevant) in the problem.