Now we use, s=ut+‌1∕2at2 For t=2s, (upward motion of ball) H=u×2+‌1∕2(−9.8)×22 ⇒‌‌H=2u−19.6...(i) For t=10s (downward motion of ball) H=u×10+‌
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(−9.8)×102 ⇒‌‌H=10u−490.....(ii) From Eqs. (i) and (ii), we have 10u−490‌=2u−19.6 ⇒‌8u‌=470.4 ⇒‌u‌=58.8m∕s Substituting u in Eq. (i) we get, ‌H=2×(58.8)−19.6 ⇒‌‌:‌‌H=98m