Question

A bird is tossing (flying to and fro) between two cars moving towards each other on a straight road. One car has speed of $27 \,km\, h^{-1}$ while the other has the speed of $18 \,km \,h^{-1}$ . The bird starts moving from first car towards the other and is moving with the speed of $36\, km \,h^{-1}$ when the two cars were separated by $36 \,km$ . The total distance covered by the bird is

• A. $28.8\,km$
• B. $38.8\,km$
• C. $48.8\,km$
• D. $58.8\,km$

Answer 1

Answer: (A)

$28.8\,km$

Answer 2

Velocity of car $A$ , $v_A = + 27\, km \,h^{-1}$ Velocity of car $B$ , $v_B = -18 \,km \,h^{-1}$ Relative velocity of car $A$ with respect to car $B$ $=v_{A}-v_{B}+27\,km\,h^{-1}-\left(-18\,km\,h^{-1}\right)=45\,km\,h^{-1}$ Time taken by the two cars to meet $=\frac{36\,km}{45\,km\,h^{-1}}=0.8\,h$ Thus, distance covered by the bird $= 36\, km\, h^{-1} \times 0.8\, h = 28.8 \,km$