Question

A Rocket works by expelling hot exhaust gases from it’s nozzle. The

exhaust gas molecules come out from the nozzle very fast hence imparting

momentum to rocket in the opposite direction. Rockets make exhaust by

burning fuel in a rocket engine. Unlike airplanes' jet engines, rockets are

designed to work in space: They don't have intakes for air, and they bring along

their own oxidizers, substances that play the role of oxygen in burning fuel. A

rocket's fuel and oxidizer—called propellants—can be either solid or liquid. The

space shuttle's side boosters used solid propellants, while many modern

rockets use liquid propellants.

A rocket's first stage gets the rocket out of the lower atmosphere. Because the

first stage must lift the entire rocket, its cargo (or payload), and any unused

fuel, it's the biggest and most powerful section. The faster a rocket goes, the

more air resistance it encounters. But the higher the rocket goes, the thinner

the atmosphere gets. The second stage has a lot less to transport, and it

doesn't have to fight through the thick lower atmosphere, so it usually has just

one engine.

Answer any four questions from five questions below -

(i) A rocket works on the principle of –

(a) Law of conservation of momentum (1)

(b) Newton’s third law of motion

(c) Newton’s second law of motion

(d) Both (a) and (b)

(ii) A propellant is a substance –

(a) Which acts as a fuel to propel the rocket

(b) Which has oxidizer along with fuel for burning it

(c) Which provides momentum to rocket during launching


(d) Which helps the rocket to burn the unused fuel

(iii) A rocket engine doesn’t have intakes or air. The possible reason for it is –

(1)

(a) It is a self propelling machine not needing air

(b) Enough momentum has been provided to it during launching

(c) It can take necessary air from atmosphere

(d) It has inbuilt oxidizers in the fuel for supporting combustion



Shown here is a graph of air density in kg/m3 with rising altitude above earth’s
surface. Based on above passage, answer the following –

(iv) In which range of altitude, a propelling rocket will experience maximum air
resistance? (1)
(a) Up to 200 km above earth’s surface
(b) Between 200 to 400 km
(c) Between 400 to 600 km
(d) Between 600 to 800 km
(v) Between 600 to 800 km, the rocket will experience – (1)
(a) Maximum air friction
(b) Variable air friction
(c) Minimum air friction
(d) Almost same air friction as between 200 to 400 km

Answer 1

Answer:

(i) A rocket works on the principle of?

answers

The rocket works because of the law of conservation of linear momentum. The law of conservation of linear momentum is very important in physics. Momentum is defined as the mass of an object times its velocity.

(b) Enough momentum has been provided to it during launching

answer For linear momentum to be conserved, the final momentum must be equal to the initial momentum, which is zero. Linear momentum is conserved if one takes into account the burnt fuel that is ejected out the back of the rocket.