Question

a body covers half of its journey with a speed of 40 m/s what es the average sped during whole journey

Answer 1

Avg speed=

total distance covered/ total time taken

Suppose the total distance=s

Time taken for first half t1=distance/speed=(s/2)/v1

=S/2v1

Time taken for second half=s/2v2

Total time=s/2v1)+(s/2v2)=s/2(1/v1+1/v2)

=S(v1+v2)/2v1v2

Avg speed= S/ total time taken

By solving this you get

Avg speed=2v1v2/(v1+v2)

So for this question=

2″40″60/100=48m/s

Short trick

Assume the distance as lcm of 40 and 60

240 total distance=240

Time taken in first half=120/40=3

Second half=120/60=2

Avg speed=total distance/total time taken

=240/5=48

Explanation:

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