A bob suspended from the ceiling of a car which is accelerating on a horizontal road. The bob stays at rest with respect to the car with the string making an angle θ with the vertical. The linear momentum of the bob as seen from the road is increasing with time. Is it a violation of conservation of linear momentum? If not where is the external force which changes the linear momentum?

A bob suspended from the ceiling of a car which is accelerating on a h

1.	A bob suspended from the ceiling of a car which is accelerating on a horizontal road. The bob stays at rest with respect to the car with the string making an angle θ with the vertical. The linear momentum of the bob as seen from the road is increasing with time. Is it a violation of conservation of linear momentum? If not where is the external force which changes the linear momentum?
Answer» No, it is not a violation of conservation of linear momentum. The external force is the force of friction of road on the car which is acting through the string of the suspended bob. In the string, it is the tension force, component of which in horizontal direction changes the linear momentum.