Question

The driver of a car driving at the speed of 88 km/h locates a bus 80 m moving ahead of him in the same direction. After 40 seconds, the bus is 120 m behind. The speed (in km/h) of the bus is:
1. 66
2. 78
3. 70
4. 75

Answer 1

Correct Answer - Option 3 : 70

Given:

Bus ahead of the car by = 80 m

After 40 seconds bus ahead of the car by = 120 m

Speed of ambulance = 88 km/hr

Formula:

Speed = Distance/Time

If speed of two persons be x km/hr and y km/hr respectively, where x > y,

Relative speed, if same directions = (x – y) km/hr

Calculation:

Let speed of bus be x km/hr

Speed of car = 88 km/hr

⇒ Relative speed = (88 – x) km/hr

Total distance covered in 40 seconds = 120 + 80 = 200 m

According to the question

(88 – x) × 5/18 = 200/40

⇒ 88 – x = 5 × 18/5

⇒ 88 – x = 18

⇒ x = 88 – 18

⇒ x = 70 km/hr

∴ Speed of bus is 70 km/hr