Everything Science Grade 11

CHAPTER 12. FORCE,MOMENTUM AND IMPULSE 12.3

Step 2 : Find the thrust of the engine

We will apply Newton’sSecond Law:

FR = ma

F 1 + Fg = ma

F 1 + (−49000) = (5000)(20)

F 1 = 149 000 N upwards

Example 12: Rockets

QUESTION

How do rockets accelerate in space?

�

F

W

tail nozzle

SOLUTION

• Gas explodes inside the rocket.


• This exploding gas exerts a force on each side of the rocket (as shown inthe picture below
  of the explosion chamber inside the rocket).

Note that the forces shown in this picture are repre-

sentative. With an explosion there will be forces in

all directions.

• Due to the symmetry of the situation, all the forces exerted on the rocket are balanced by
  forces on the opposite side, except for the force opposite the open side. This force on the
  upper surface is unbalanced.