A ball projected from ground vertically upward is at same height at time t1 and t2 . the speed of projection of ball is

Suppose the height travelled by ball in the time t1 and t2 is h.
and the speed of projection is u.
Then, using relation
s=ut+12at2We have,h=ut1-12gt12and h=ut2-12gt22(Acceleration is taken negative as it acts downwards i.e opposite direction of motion)so, ut1-12gt12=ut2-12gt22 ut1-ut2=12gt12-12gt22u(t1-t2)=12g (t12-t22)u=g (t12-t22)2(t1-t2)=g((t1+t2)2

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