Q. 19

# A bird is tossing (flying to and fro) between two cars moving towards each other on a straight road. One car has a speed of 18 m/h while the other has the speed of 27km/h. The bird starts moving from first car towards the other and is moving with the speed of 36km/h and when the two cars were separated by 36 km. What is the total distance covered by the bird? What is the total displacement of the bird?

Answer :

Speed of car 1 = 18 km/h

Speed of car 2 = 27 km/h

Relative speed of the cars = (18+27) = 45 km/h. (since they both are moving in the same direction)

Total distance between the cars = 36 km/h.

Time taken to cover the distance = Total distance / Relative Speed = 36/45 = 0.8 hours

Distance covered by the bird in 0.8 hours = Speed x Time = 36 x 0.8 = 28.8 km

Displacement will be the distance between the starting point and the point of meeting of the cars.

Since the cars meet in 0.8 hours, the distance from the starting point will be 18 x 0.8 = 14.4 km. (The bird starts from the car running at 18 km/h). Thus, the displacement of the bird is 14.4 km.

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A ball falls on the ground from a height of 2.0 m and rebounds up to a height of 1.5 m. Find the coefficient of restitution.

HC Verma - Concepts of Physics Part 1