A group of people are marching with a speed of 5 m/s. The distance between the first and last row is 100 m. A dog starts running from the last row and moves towards the first row, turns and comes back to the last row. If the dog has travelled 400 m, find the speed of dog ?

thank you kumar

a is d answer..

while moving same direction,
group will cover x mtre with 5 m/s
and dog , 100+x m with 's' m/s
time will be same,so
x/5 = (100+x)/s -------(a)

while in opp. direction,
time taken, t= 100/(5+s) -------------(b)

400 total distance covered by dog
100+x moving same direction
100-5t moving opp. direction

so,
400 = 100 + x + 100 - 5t put x & t from (a) n (b),

you ll get the answer..
Thanks :)

Thank you @Kumar.

@Sagun, Can you give your explanation?

There are some more new questions have been posted. Move on that. Come friends.

Thank you Sagun and Kumar

A

Suppose the dog's speed is S while running towards the front row, Then, The relative speed of Dog with respect to marching the marching people, = S - 5 [As both are moving in same direction.] so, The dog will reach at the front row after time, T = 100/(S - 5) ----------- (1)
While running towards the last row, the relative speed with respect to the marching people,
= S + 5 And,
The dog will reach at the last row after time, t = 100/(S+5) ------------ (2)

Total time, T + t = [{100/(S - 5)} + {100 /( S + 5)}] = 200S /(S^2 - 25) ------------ (3)

Total distance Covered By Dog,

S*(T + t) = 400 S * ( 200S/S^2 - 25) = 400

S = sqrt (50) S = 5 *Sqrt(2).

Is it clear? Any one has any other approach? Please, give your approach to solve this question in easy way.

Yours Welcome!!!!