Frames of reference and vectors problem

Homework Statement

A car is moving toward north with a speed of 35 km/h. A truck travels toward west with a speed of 42 km/h.
Which is the speed of the caravan according to the car's driver?

The Attempt at a Solution

The solution given by the book is 15 m/s with direction south-west, but I get the solution of 15 m/s with direction north-west and I cannot get the reason.
Can you help me with this?
Thanks

stockzahn
Homework Helper
Gold Member
Please show or describe your calculation/drawing, which gave you the results (15 m/s, NW).

I used Pitagora theorem to get the value of 54 km/h that is 15 m/s, but the direction of the vector is north-west and not south-west.

stockzahn
Homework Helper
Gold Member
You've already got the velocity correct in the first place, the direction is correct like the book says (SW). Did you try to solve the (direction-)problem graphically or numerically? Please show me your attempt to be able to help you.

Mark44
Mentor

Homework Statement

A car is moving toward north with a speed of 35 km/h. A truck travels toward west with a speed of 42 km/h.
Which is the speed of the caravan according to the car's driver?
Does "caravan" refer to the truck? In British English, a caravan is a trailer. In American English, a caravan is a collection of vehicles (also animals) that are traveling as a group.

The truck is roughly SW of the car. Perhaps the question could be rephrased as "how fast is the distance from the car to the truck changing?"
notsoclever said:

The Attempt at a Solution

The solution given by the book is 15 m/s with direction south-west, but I get the solution of 15 m/s with direction north-west and I cannot get the reason.
Can you help me with this?
Thanks