# Can you combine two accelerations together?

1. Jul 17, 2015

### Zynoakib

When I was doing an exercise on projectile motion, there was a question that asked something like the max. altitude reached by an accelerating rocket. After some calculations, I got 23.96ms-2 as the vertical acceleration, then I minus it with 9.8ms-2 (gravitational acceleration as the two accelerations, I thought, should work against each other). Turns out, this is wrong and I should calculate the rest with 23.96ms-2 as the vertical acceleration. So my question is, why am I not supposed to minus 23.96 with 9.8? Because you can combine tangential acceleration and radial acceleration together to give a "resultant acceleration", but why is it not my case?

Thanks!

2. Jul 17, 2015

### Puma

I think you'll have to post the original question to get a clear reply. All that comes to mind is that gravity had already, in some way, been accounted for.

3. Jul 17, 2015

### Zynoakib

Question 65

4. Jul 17, 2015

### Staff: Mentor

As Puma suggested, the acceleration given in the problem is the actual acceleration of the rocket, not the thrust of the engine.

5. Jul 17, 2015

### Zynoakib

Thank you guys!