Question

A train start from station A and moves with constant acceleration, then with constant speed and finally with constant retardation. If the ratio of time taken are 1 : 6 : 2 and maximum speed of train is 72 km/h. Then the average speed for the whole journey is –

• A. 60 km/h
• B. 54 km/h
• C. 72 km/h
• D. 20 m/s

Answer 1

Answer: (A)

60 km/h

Answer 2

Displacement of train = Area of trapezium

= $\frac{1}{2}$ × (9t + 6t) × 72

 $\bar{v}$= $\frac{Displacement}{Time}$ = $\frac{\frac{1}{2} \times (15t) \times 72}{9t}$

= 60 km/h