Question

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Answer 1

when the projectile is launched and also when it hits the ground h(t) = 0 so we have
-40t^2 + 200t = 0
-40t(t - 5) = o

so t = 0 and t = 5
5 is the times when it land after the flight
answer t seconds.

Answer 2

We want to find h(t) = 0 because the height is 0 when the projectile hits the ground.

-40t^2 + 200t = 0

40t^2 - 200t = 0

t^2 - 5t = 0

t(t - 5) = 0

So, t = 0 or t = 5. But t = 0 is when the projectile is launched. So, t = 5.

The answer is C.