A model rocket is launched from the roof of a building at 30 meters per second . The height of the building is 10 meters.

Question

1. what Is the rocket’s maximum height?
2. after how many seconds does the rocket reach its maximum?
3. when is the rocket at 10 meters?
4. when does the rocket hit the ground?

Answer 1

I have previously answered a similar question. So, will give a general outline of the approach.

Use the conservation of energy principle. At the base, when the rocket is launched, the energy is a combination of potential energy due to height above ground and kinetic energy due to launch speed.

At the maximum height before rocket starts to drop back, the speed is zero. Entire energy is potential energy. Assume that the rocket reaches height h (with reference to the ground). Then

mg*10 + 1/2*m*(30)² = mg*h

Using the known values of g you can calculate h.

To calculate times, use the newton's equation of motion

h = ut + 1/2*g*t²

Note that the speed u is different when the rocket is shot up, and when it starts to fall back. So use the equation carefully to answer different parts of the question.