Gravitational acceleration problem

[Kenny Wong]

Homework Statement

Alice and Bill are at the top of a building. Alice throws her ball downward. Bill simply drops his ball. Which ball has the greater acceleration just after release?

Homework Equations

force, F=ma and F=mg

The Attempt at a Solution

Alice: F=ma+mg=m(a+g)
Bill: F=mg
Alice's ball has a greater acceleration.
I AM WRONG. WHY?

 

[gneill]

Homework Statement

Alice and Bill are at the top of a building. Alice throws her ball downward. Bill simply drops his ball. Which ball has the greater acceleration just after release?

Homework Equations

force, F=ma and F=mg

The Attempt at a Solution

Alice: F=ma+mg=m(a+g)
Bill: F=mg
Alice's ball has a greater acceleration.
I AM WRONG. WHY?

After Alice releases the ball, what's producing that acceleration "a" that you put in your equation?

 

[Kenny Wong]

Because Alice throws instead of releases, an extra force is exerted downwards?

 

[gneill]

Because Alice throws instead of releases, an extra force is exerted downwards?

Bill drops, Alice throws. But both release, otherwise they'd still be holding onto their balls. You're meant to consider the portion of the trajectories when they are no longer in contact with their ball.

 

[Sharath K Menon]

The acceleration for both of them should be the same.
An acceleration is produced only when there is an external forces is applied.
after release, the only force on the balls is tat of gravity.
Thus the acceleration will be the same for both of them.

Alice's ball has more acceleration only during the time when she is throwing the ball and excerting force, she gave it an initial velocity. After the ball leaves her hand, only gravity acts on it.