Answer to Question #215938 in Mechanics | Relativity for Zoe

Question

Determine which of the following moving objects obeys the equations of projectile motion: (A) A ball is thrown in an arbitrary direction. (B) A jet airplane crosses the sky with its engine thrusting the plane forward. (C) A rocket leaves the launch pad. (D) A rocket moves through sky after its engines have failed. (E) A stone is thrown under water. 

Answer 1

(A) A ball thrown arbitrarily has only the gravitational force acting on it. The ball moves with the initial velocity supplied by the boy. Since the motion is under the influence of gravity alone, the equations of projectile motion are obeyed in this case.

(B) In the case of the jet airplane with engines thrusting the plane, there is another force acting on the plane other than gravity and hence the equations of projectile motion are not obeyed in this case.

(C) For a rocket leaving a launch pad, the forces acting on the rocket are in opposite direction to that of gravity. Hence, the equations of a projectile are not obeyed here.

(D) In the case of a rocket after its engine fails, the rocket now moves with the influence of alone using the initial velocity provided by the engine before it failed. Hence, the equations of a projectile are obeyed here.

(E) The underwater motion of any object is influenced by buoyancy and other forces. Therefore, the equations of a projectile are no-followed here.

Thus, option (A) and (D) follows the equations of projectile whereas option (C), (D), and (E) do not.