Question

16. A motor car starts with the speed of 70 km/hr with its speed increasing every two
hours by 10 kmph. In how many hours will it cover 345 kms? (Bank P.O. 2003)
(a) 2- hrs
(d) Cannot be determined
(b) 4 hrs 5 min
(e) None of these
(c) 4hrs​

Answer 1

Answer:

(e) None of these

Step-by-step explanation:

To find -

Find time ,

Solution :-

Starting speed = 70 km/hr

In first two hours it is = 140 km

For next two hours ,

Speed increased 10 km/hr

→ 70 + 10 = 80 km/hr

For two hours = 80 km

Hence,

Total distance now = 140 +160 = 300 km

Hence,In time of 4 hours it covers 300 km.

Now speed is 90 km/hr

It will take in half hour 45 km remaining to covers it 90 km/hr

Hence ,

It need 4 hours 30 minutes to covers 345 km.

Answer 2

Answer:

Step-by-step explanation:

use the formula s = ut + 1/2 at^2

s = 345 km

u = 70 kmph

a = 10/2 = 5 km/h^2

=> 345 = 70t + 1/2 * 5 * t^2

multiply the equation by 2

=> 690 = 140t + 5t^2

=> 5t^2 + 140t - 690 = 0

divide the equation by 5

=> t^2  + 28t - 192 = 0

solving it you get t = 12 and t=16

therefore the answer is none of these