[2D projectile problem]: Rocket being launched

[hiuting]

Homework Statement

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.

Homework Equations

Kinematics equations (along x and y)

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=V_{0[SUB/]sin70 and acceleration=8sin70.}

 

[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?

 

[hiuting]

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

 

[Delphi51]

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

 

[flatmaster]

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?

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