Ncert Exercises & Solutions

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 km/h while the other has a speed of 27 km/h. The bird starts moving from the first car towards the other and is moving with the speed of 36 km/h and when the two cars were separated by 36 km. What is the total distance covered by the bird?

Hint: Apply the concept of relative motion.

Step 1: Find the time of meeting the car.

Given Speed of first car = 18 km/h

Speed of second car = 27 km/h

$∴$ Relative speed of each car w.r.t. each other
= 18 + 27 = 45km/h

Distance between the cars = 36 km

$∴ Time of meeting the cars (t) = \frac{Distance between the cars}{Relative speed of cars} = \frac{36}{45} = \frac{4}{5} h = 0 .8 h$

Step 2: Find the distance covered by the bird in time which is equal to the time of meeting the car.

$\begin{array}{l} Speed of the bird (v_{b}) = 36 km / h \\ ∴ Distance covered by the bird = v_{b} \times t = 36 \times 0 .8 = 28 .8 km \end{array}$

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