A particle moves half the distance with velocity u. Rest of the half distance is covered with velocities v1 and v2 in equal intervals of time. Find the average velocity of the particle.
A
2u(v1+v2)2u+v1+v2
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B
2u(v1+v2)u+v1+v2
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C
2u(v1+v2)u+2(v1+v2)
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D
u+v1+v222
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Solution
The correct option is A2u(v1+v2)2u+v1+v2 Motion of the particle is shown above.
Let the total distance covered by the particle be s.
For second half motion :
Distance covered x+y=s2 .....(1)
Equal interval of time is taken to cover x and y distances with speed v1 and v2, respectively. ⇒xv1=yv2
⇒xv2=yv1
⇒(s2−y)v2=yv1 (using 1)
⇒s2v2=y(v1+v2)
⇒y=sv22(v1+v2)
From (1), we get x+sv22(v1+v2)=s2 ⇒x=sv12(v1+v2)
Time taken to cover second half motion, t=xv1+yv2=s(v1+v2)
Time taken to cover first half motion, t′=s/2u=s2u Now average velocity Vavg=TotaldistanceTotaltime ∴Vavg=ss2u+s(v1+v2) ⟹Vavg=2u(v1+v2)v1+v2+2u