Answer to Question #302447 in Mechanics | Relativity for cin

Question

A projectile is fired at an angle of 30° above the horizontal from the edge of a vertical cliff. Ignore

air resistance. (a) Is the projectile’s velocity ever only horizontal? If so, when; if not, why not?

(b) Is its velocity ever only vertical? If so, when; if not, why not? (c) Are there any points at which

the projectile’s acceleration is either parallel or perpendicular to its velocity? Explain.

Answer 1

Explanations

• Since the projectile is fired up with an angle to the horizontal, its instantaneous velocity always carries 2 components namely horizontal and vertical.
• So there is no point in the projectile that the velocity becomes solely vertical as there is always the unchanged horizontal component which then leads the instantaneous velocity to have an inclined direction.
• The horizontal velocity however can become the sole velocity the object has only at the topmost point of the trajectory where the vertical component becomes momentarily zero leaving the horizontal component alone.

• Finally, it is the topmost point of the trajectory where the acceleration is perpendicular to the velocity.
• Actually, the velocity itself gets positioned perpendicular to the acceleration as the acceleration is always vertically downwards.