A projectile is launched vertically upward at 40 m/s. If air resistance is negligible, its speed upon returning to its starting point is
A)less than 40 m/s.
B)40 m/s.
C)more than 40 m/s.
All along the ball's trajectory, its acceleration is
D)g downward.
E)g at an angle.
F)zero.
If air resistance does affect motion, then the ball's speed upon returning to its starting point is
G)less than 50 m/s.
H)50 m/s.
I)more than 50 m/s.

Question

Quizplus · Accepted Answer

In the absence of air resistance, the speed of the projectile when it returns to its starting point will be the same as its initial speed, 40 m/s, due to the conservation of energy. The acceleration all along the ball's trajectory is g downward, due to gravity acting on it. If air resistance does affect motion, the ball's speed upon returning to its starting point will be less than its initial speed due to the energy lost to air resistance, making it less than 50 m/s, even though the initial speed was only 40 m/s; the reference to 50 m/s seems to be a distractor.

A Projectile Is Launched Vertically Upward at 40 M/s