- #1

Newlander

- 6

- 0

## Homework Statement

"A ball is thrown straight upward with a velocity of 18 m/s. How much time passes before the ball strikes the ground? Disregard air resistance."

v

_{i}= 18 m/s

a = -9.8 m/s

^{2}

t = ?

[not sure: v

_{f}= 0 m/s]

## Homework Equations

v

_{f}= v

_{i}+ at

## The Attempt at a Solution

v

_{f}= v

_{i}+ at

t = [(v

_{f}- v

_{i})/a]

t = [(0 m/s - 18 m/s)/-9.8 m/s

^{2}] = 1.8 s

Concerns:

--First, I understand that if I have final velocity as 0 m/s, that refers to when the ball has reached its maximum height--not its pre-impact final velocity.

--Second, with the first comment in mind, I'm not sure my approach is appropriate for this particular problem--and would appreciate guidance if it's not.

--Third and finally, some of my classmates insist that the correct answer is about double the answer I arrived at because "you just multiply the answer by 2 since it's only gone half of the distance" as I have conveyed above. I understand this thinking to some degree, but its simplicity seems to suggest the ball is projected from the ground--rather than simply thrown from what I'm gathering is knee-height. I would love to get your thoughts.