Initial velocity of rocket,
u=0m∕ s acceleration,
a=20m∕ s2 Upward velocity of rocket at the end
5 s,
v=u+at=0+20×5=100m/ s Distance travelled by rocket in
5 s,
s1=at2=×20×52=250m After
5 s, rocket moves under the effect of gravitational acceleration and with initial velocity of
100m/ s.
∴ Distance travelled by rocket in this situation is
s2, then using equation,
v2=u2−2gs2 ∴ Total upward distance covered by rocket,
s=s1+s2=250+500=750m Now, rocket starts falling from this height and if
v′ be the velocity of rocket when it reaches at ground, then
(v′)2=u2+2gs=0+2×10×750=15000⇒v′=√15000=50√6m/ s