Total time taken to reach the ground T=t1+t2+t3 u=80m/s
Velocity of the bullet at point A VA=0m/s a=10m/ V=u+at 0=80−10t1 t1=8s t2=t1 (as there is no air resistance) Calculation for t3 Velocity of the bullet at point B, VB=u=80m/s h=400m Using s=ut+
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2
at2 ⇒400=80×t3+
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×10×t32 ⇒5t32+80t3−400=0 ⇒t32+16t3−80=0 ⇒t3(t3+20)−4(t3+20)=0 t3=−20sort3=4s Time cannot be negative hence neglecting t3=−20s Total time T=8+8+4=20s