The accelerometer glued to the mountain will show -9.8m/s^2, not zero. The one glued to the rocket will show the same. The force of the rocket thrust is the opp

The accelerometer glued to the mountain will show -9.8m/s^2, not zero. The one glued to the rocket will show the same. The force of the rocket thrust is the opposite of the force of the glue holding it to the mountain, so the sum results in zero additional acceleration.