Question

A bullet is fired from the tank at some angle with the horizontal. Assume air resistance is negligible. Choose the correct option which is not constant throughout the flight of the projectile.

A) Horizontal velocity
B) Vertical velocity
C) Horizontal acceleration
D) Vertical acceleration
E) Angle at which the projectile is launched

Answer 1

This problem can be solved by recalling the forces acting upon a body in projectile motion. It is subjected only to the downward force of gravity and no other forces in any other direction. This force of gravity produces a corresponding vertical acceleration in the projectile.

Complete answer:
For a body in projectile motion, the only force acting on the projectile in the absence of air resistance is the downward force of gravity. Therefore, a subsequent vertical acceleration is produced in the projectile but no such horizontal acceleration is produced as there is no force acting in the horizontal direction.
Now, let us analyze the options one by one.
(a) The horizontal velocity of the projectile remains constant. This is because there is no acceleration of the projectile in the horizontal direction because there are no forces on the projectile in the horizontal direction.
(b) The vertical velocity of the projectile does not remain constant. This is because there is a vertical acceleration of the projectile in the downward direction which is the acceleration due to gravity. This acceleration changes the vertical velocity of the projectile throughout its flight.
(c) The horizontal acceleration of the body remains constant and equal to zero as there are no forces acting on the projectile in the horizontal direction.
(d) The vertical acceleration of the body remains constant through its motion and equal to the downward acceleration due to gravity since the only force acting on the body is in the vertically downward direction, the force of gravity.
(e) The angle at which the projectile is launched is an initial parameter that is not changed throughout its flight.
Therefore, only the vertical velocity of the projectile does not remain constant throughout its motion.

Therefore, the correct option is B) Vertical velocity.

Note:
Students must note that in this question, we were asked to neglect air resistance. However, if that was not the case, then there would have been a force on the projectile in the horizontal direction also. This force will be the drag force offered by the air. This force would produce a respective horizontal acceleration in the projectile and subsequently, the horizontal velocity of the body would then not remain constant and be changing throughout its flight.