Question

A car cover first half of the total distance with speed 30km and second half with speed of 54 km per hour find the average speed of the car

Answer 1

average speed = total distance /total time


let d be the total distance , t1 be the time taken to cover 1st half and t2 be the time taken to cover 2nd half

t1=d/2(30)=d/60

t2=d/2(54)=d/108

average speed = d/d(1/60+1/108)

=540/14=270/7kmph


I hope this will help u:)

Answer 2

We know that the formula to find time = Distance/Speed

Using it :

Let the total distance be = d

Then it is given that the speed for the half distance = 30 km

Then , time taken to cover half distance (that one in which the speed was 30km/h) =

$t = \frac{d}{2 \times 30} = \frac{d}{60}$

Then , time taken to cover half distance (that one in which the speed was 54km/h) =

$t = \frac{d}{2 \times 54} = \frac{d}{108}$

So we know that

Average Speed = Total Distance Covered /Total Time Taken

$\frac{d}{ \frac{d}{60 } + \frac{d}{108} } \\ \\ = \frac{d}{ \frac{1}{60} + \frac{1}{108} } = \frac{540}{14} \\ \\ = \frac{270}{7} = 38.57 \: km \: per \: hour$

What is average speed ?

=> The average speed of a body is defined as the ratio of the total distance covered by the body and the total time taken.

And, what is speed?

Speed of a moving body is the distance travelled by the body in the unit time.