Hello, usm_67!

When the rocket hits the ground, .A model rocket is launched from the roof of a building.

Its flight path through air is modelled by

where is height of the rocket above ground in metres and is the time after the launch in seconds.

(a) When will the rocket hit the ground?

Solve: .

Divide by -5: .

Quadratic Formula: .

Therefore: . seconds.

When is(b) When is the rocket 45m off the ground?

Solve: .

We have: .

Quadratic Formula: .

Therefore: . seconds.