Question

A motor starts with the speed of 70 Km/hr with its speed increasing every two hours by 10 Kmph.In how many hours it will cover 345 kms ?

Answer 1

the answer is 4hr and 30 mins

see to understand this first make a long line and plot points ABCD in some intervals

this will represent the journey

on the a write 70 it's the speed

time to reach a to b is 2

bcoz every 2 HR the speed increases

you know the formula speed =distance/time

so put the value and find the distance

you will get 140 km

now on b write 80km/HR

same the time required to reach c will be 2 HR

distance will be 160km

now on c write 90km/HR

same it will cover 450 km in 2 HR

now we want to find the time to cover 345 km

so if you add the distance of a to b and b to c you will get 300km we want 45km more so mark a point between c and d

of 45 km

now you know the speed i.e 90 you know distance i.e 45km apply formula and find time you will get 1/2 which means 30 mins

do add the time of covering the distance ab,bc and ce

you will get 2+2+30min

i.e 4hr 30 mins

Answer 2

here, acceleration =

$10 \frac{km}{ {hr}^{2} }$

speed =

$70 \frac{km}{hr}$

using second equation of motion v get,

$345 = (70) \times t + \frac{10 \times {t}^{2} }{2} \\ or \\ {t}^{2} + 14t - 69 = 0 \\ on \: solving \: we \: get \\ t = 3.863 hrs$