Question

A bus completes a journey in 15 hours at a speed of 72km/hr.in order to cover the same distance in 12 hours , the speed of the bus must be increased by

Answer 1

Distance travel is same so,
u1t1+1/2gt1^2=u2t2+1/2gt2^2
72×15+1/2g15×15=u12+1/2g12×12
1080+1125=12u+570
2205-570=12u
1635=12u
U=136.2km/h
And speed increased by=136.2-72
=64.2km/h

Answer 2

Answer: The speed of bus should be increased by 18 km/hr.

Explanation:

Given that,

Total time = 15 hours

Speed = 72 km/hr

We know that,

The distance is the product of the speed and time.

$D = v\times t$

$D = 72\times 15$

$D = 1080 km$

If cover the same distance in 12 hours

The speed will be

$v = \dfrac{1080}{12}$

$v =  90 km/hr$

The speed of bus must be increased by

$v = 90\ km/hr-72\ km/hr$

$v = 18\ km/hr$

Hence, The speed of bus should be increased by 18 km/hr.