Question

7. A motor cyclist goes from station A to B at 40 km h ' and
then returns from B to A at 120 kmh-. Calculate (i) average
speed (ii) average velocity during the round trip.
[Ans. (i) 60 km h-(ii) zero]
3​

Answer 1

Acc. To me,

Answer is a) 60 km/h  b) 0

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A) s1(speed of going)=40km/h

s2(speed of returning)=120km/h

d=x km

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Here i derive formula if you don't want derivation then use formula that is in  eq 3

Avg speed =total distance/total time

Total d=d+d(for going and returning) and d is same

total time=t1+t2(for going and returning)

You don't know time so find out by

s=d/t

For t1(going)

s=s1,d=d,t=t1 so

t1=d/s1---------1

Here for t2(returning)

s=s2,d=d,t=t2

t2=d/s2------------2

Put it and find

avg S=2d/t1+t2

avg S=2*s1*s2/s1+s2------3

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Put s1 and s2 in equation 3 and find

Avg S=60 km/h

B) Average velecity =Total displacement /total time

Here cyclist go an return to same place so displacement is zero

If you put displacement =0

then velocity =0