Q1.
What will happen if the engine of a rocket moving in the space, fires in the direction of its motion?
Answer
The rocket slows down.
Exhaust gas is thrown out forwards (along the direction of motion)
By Newton's third law, the gas pushes the rocket backwards
Net force on the rocket is opposite to its velocity
→ acceleration is negative (retardation) → speed decreases
By Newton's third law, the gas pushes the rocket backwards
Net force on the rocket is opposite to its velocity
→ acceleration is negative (retardation) → speed decreases
Why it happens: a rocket engine does not push against anything outside — it works purely by throwing mass in one direction and receiving an equal push in the other. Point the exhaust forwards and the reaction force points backwards, which is a retarding force. This is the only way to brake in space, where there is no air and no ground to push against.
Did you know? The Vikram lander of Chandrayaan-3 used exactly this method to slow down and reach the velocity needed for a soft landing near the south pole of the Moon.