Question

ASSERTION
Rocket in flight is not an illustration of projectiles.
REASON
Rocket takes flight due to combustion of fuel and does not move under the gravity effect alone.
A) Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
B) Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
C) Assertion is correct but Reason is incorrect
D) Both Assertion and Reason are incorrect

Answer 1

Hint: Recall the definition of projectile motion. In rocket propulsion the speed of the rocket is not constant and it keeps changing. In projectile motion the only force acting is gravity.

Complete solution:
In projectile motion, the object is given an initial velocity at an angle and no internal engine is present to change the velocity or direction of the object. Also, in projectile motion the air resistance is neglected.
In the motion of a rocket, the rocket keeps changing its speed and direction by changing the amount of fuel it burns and by navigation system. This is in contradiction to projectile motion. Also, the path of the rocket is non-parabolic, it can trace any path which can change dynamically as per the needs.
Hence the ASSERTION is Correct. Rocket in flight is not an example of projectile.
During its flight, a rocket is subject to four forces: weight, thrust and aerodynamic forces, lift and drag. The weight force of the rocket is always directed towards the center of the Earth.
The magnitude of thrust depends on the mass flowing out and velocity and pressure at the exit of the nozzle. The thrust normally acts along the longitudinal axis of the rocket and therefore acts through the center of gravity. Lift again depends on various factors such as density of air, velocity, shape of body, surface area through which the air flows, etc.
Drag force is experienced when a body moves through any fluid. Here air is the fluid.
From the above points, it is clear that the rocket does not move under the effect of gravity alone.

Therefore, the given REASON is also correct. (A) is the correct option.

Note: It is important to have knowledge of all the force acting on the rocket during its motion, in order to answer this question. Also, don’t forget that lift force also acts on the rocket throughout the motion. It is also important to note that the drag force is generally neglected in all projectile motion while solving problems at lower level. This drag force always exists in real life scenarios.