Question

In Burj Khalifa, A is descending from 151 St floor by lift with a speed of 6 floors per second while B is ascending from 1 St floor by lift with a speed of 4 floors per second. After what time both A and B will meet?

Answer 1

Answer:

15.1 seconds

Step-by-step explanation:

Let Distance between consecutive floors is 1 meter

Let After time "T" A and B meets

Let B covered the X meter distance from 1 St Floor in time T

Then

Distance covered by A in time T from 151 floor = ( 151 - X ) m

Now

We are given that

Velocity of A = 6 floors per second = 6 m/s

Velocity of B = 4 floors per second = 4 m/s

Since

A and B reaching to each other

So

Combined velocity of A and B = V = 6 + 4 = 10 m/s

Combined Distance Covered by A and B = D = X + 151 - X = 151 m

We know that

Velocity = Distance / time

Putting values we get

         V = D / T

  ⇒  10 = 151 / T

  ⇒    T = 151 / 10 = 15.1 s

 ⇒    T = 15.1 sec

So after passing 15.1 second A and B meets

-------------------------------End----------------------------------------

(The question is end here but we check the solution for you)

Checking of answer

since

distance of B = X = velocity of B × time = 4 × 15.1 = 60.4 m

distance of A = velocity of A × time = 6 ×15.1 = 90.6 m

and

Distance of A and B = 60.4 + 90.6 = 151 m

hence our calculation are true