The truck is moving at a speed of 60 km / h. The driver sees that in relation to his car

| September 22, 2021 | education

The truck is moving at a speed of 60 km / h. The driver sees that in relation to his car, the passenger car went to overtake at a speed of 20 km / h. What is the speed of a car relative to the road?

Vg = 60 km / h.

Vlg = 20 km / h.

Vl -?

According to the law of relativity of velocities, the speed of a body relative to a stationary frame of reference Vn is the vector sum of the speed of a moving frame of reference relative to a stationary Vn and the speed of a body relative to a moving frame of reference Vn: Vn = Vn + Vn.

The fixed frame of reference is the earth, the movable frame of reference is the truck.

Therefore, the speed of the truck relative to the ground Vg, is the speed of the moving frame of reference Vnp: Vnp = Vg.

The speed of overtaking is easy Vlg, is the speed of the body, relative to the moving frame of reference Vp: Vp = Vlg.

The speed of a passenger car relative to the ground Vl, is the speed of a body relative to a stationary frame of reference Vn: Vl = Vn.

Vl = Vg + Vlg.

Vl = 60 km / h + 20 km / h = 80 km / h.

Answer: a passenger car is moving at a speed of Vl = 80 km / h.



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