# [2D projectile problem]: Rocket being launched

1. Oct 25, 2009

### hiuting

1. The problem statement, all variables and given/known data
A rocket launched at 70 degrees to the horizontal has a constant net acceleration of 8m/s^2 along this direction for 6.5s and then is in free-fall.

Find: (a) the maximum height; (b) the horizontal range.

2. Relevant equations
Kinematics equations (along x and y)

3. The attempt at a solution
I know that at the initial position, along x: position=0, velocity=V0cos70 and acceleration=8cos70. along y: position=0, velocity=V0[SUB/]sin70 and acceleration=8sin70.

2. Oct 25, 2009

### Delphi51

It looks to me like the rocket initially has zero speed. It burns for 6.5 s, accelerating at 8 m/s². You'll also have to consider the acceleration of gravity during those 6.5 s. So, can you come up with the velocities and distances at the end of the 6.5 s?

3. Oct 25, 2009

### hiuting

Thanks :)
I got it! ... after the 6.5s, the rocket keeps moving right? till V=0?

4. Oct 25, 2009

### Delphi51

Yes, the maximum height will be where Vy = 0.
It is just a standard projectile problem after the high acceleration phase.

5. Oct 25, 2009

### flatmaster

The problem statement says the NET acceleration is 8m/s^2, so gravity is already taken into account.