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 separted by 36 km. What is the total distance covered by the bird? What is the total displacement of the bird?
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Answered by
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The total time duration For the two cars to meet
= total distance/relative velocity
= 36 km / (18+27) kmph = 4/5 hours
In this duration, the 1st car travels : 4/5 hr* 18 kmph = 14.4 km
That is the meeting point.
In this time period, the bird could travel : 4/5 hr * 36 kmph = 28.8 km
This is the total distance travelled by the bird. ..
displacement from starting position will be = distance of the meeting point from the starting point of 1st car: 14.4 km
=======================================
alternately,
Bird meets car2, after t = 36/63 hr = 4/7 hr
At this time distance between car1 and bird/car2: 4/7 *(36-18)=72/7 km
Bird meets car1 after : (72/7) / 54 hrs = 4/21 hrs ie., at total time 16/21 hrs total
The distance between bird/car1 and car2 is now: 36 - (16/21)*45 = 12/7 km
Bird meets car2 now after (12/7) km/63 kmph = 4/147 hrs at time total = 116/147 hrs
Now the distance between Bird/Car2 and car1 will be: 36 - 116/147 * 45 = 72/147 km
Bird meets car1 now after: (72/147) / 54 =4 / 441 hrs at total time: 352/441 hrs
Now distance between car1/Bird and car2 is: 36 - 352/441 * 45 = 12 /147
The shuttling durations of bird are: 4/7, 4/21, 4/147, 4/441,
Distance 36, 12/7 , 12/147
Total of the shuttling times = 4/7 + 4/147 + ... + 4/21 + 4/441+...
= (4/7) / [1 - 1/21] + (4/21) / [1 - 1/21]
= 3 / 5 hrs. + 1/5 hrs = 4/5 hours
Total distance travelled by bird: 4/5 hrs * 36 kmph = 28.8 km
= total distance/relative velocity
= 36 km / (18+27) kmph = 4/5 hours
In this duration, the 1st car travels : 4/5 hr* 18 kmph = 14.4 km
That is the meeting point.
In this time period, the bird could travel : 4/5 hr * 36 kmph = 28.8 km
This is the total distance travelled by the bird. ..
displacement from starting position will be = distance of the meeting point from the starting point of 1st car: 14.4 km
=======================================
alternately,
Bird meets car2, after t = 36/63 hr = 4/7 hr
At this time distance between car1 and bird/car2: 4/7 *(36-18)=72/7 km
Bird meets car1 after : (72/7) / 54 hrs = 4/21 hrs ie., at total time 16/21 hrs total
The distance between bird/car1 and car2 is now: 36 - (16/21)*45 = 12/7 km
Bird meets car2 now after (12/7) km/63 kmph = 4/147 hrs at time total = 116/147 hrs
Now the distance between Bird/Car2 and car1 will be: 36 - 116/147 * 45 = 72/147 km
Bird meets car1 now after: (72/147) / 54 =4 / 441 hrs at total time: 352/441 hrs
Now distance between car1/Bird and car2 is: 36 - 352/441 * 45 = 12 /147
The shuttling durations of bird are: 4/7, 4/21, 4/147, 4/441,
Distance 36, 12/7 , 12/147
Total of the shuttling times = 4/7 + 4/147 + ... + 4/21 + 4/441+...
= (4/7) / [1 - 1/21] + (4/21) / [1 - 1/21]
= 3 / 5 hrs. + 1/5 hrs = 4/5 hours
Total distance travelled by bird: 4/5 hrs * 36 kmph = 28.8 km
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