Question

A car moves on a straight road for first half time with the constant
speed of 20 m/sec. and the next half time with a constant speed of 60
m/sec, then calculate average speed.​

Answer 1

Answer:

Av. Speed = 40 m/s

Explanation:

Let the total time taken be T

Now,

Average Speed = Total Distance/Total Time

But here we have a bonus, we need not rely on distance and time, If the car moves with speed a in half time, then speed be in the next, then the average speed = (a + b)/2

But let's go the original way,

In half time Car travels with 20m/s

Thus,

Speed = Distance/Time

Distance covered = Speed × time

D = 20 × T/2

D1 = 10T m

Now,

Car moves with 60 m/s in the next half time,

Thus, Distance = 60 × T/2

D2 = 30T

Now,

Average speed = (D1 + D2)/T

Av. speed = (10T + 30T)/T

Av. Speed = 40T/T

Av. Speed = 40 m/s

which was equal to (20 + 60)/2 = 80/2 = 40 m/s

Always Remember to do it in D/T way because in some cases (v1 + v2)/2 may not be applicable.

Hope it helped and you understood it........All the best