# Homework Help: Statement about ball thrown upwards

1. Oct 10, 2012

### chewchun

1. The problem statement, all variables and given/known data
A ball is thrown vertically upwards and air resistance is NOT negligible.Which of the folloiwng statement is incorrect.
A:At maximum height,acceleration is zero.
B: Time taken for ball to travel upwards is shorter than time taken to travel down
C: Distance traveled for upward and downward motion are the same.
D: Magnitude of acceleration for the upward motion is always greater than 9.81ms-2

2. Relevant equations

3. The attempt at a solution
I choose A instantly as i knew there is acceleration downwards due to gravity.I was right though.
But i have no clue why D is correct?If a ball is facing air resistance wouldn't it slow down(Net force is pointing towards Earth)?

2. Oct 10, 2012

### SHISHKABOB

so when the ball is going upwards, what are the forces acting on it

3. Oct 10, 2012

### chewchun

Downward:
Resistive force due to air resistance
Gravitational force due to gravity
Upward:
Zero?

4. Oct 10, 2012

### SHISHKABOB

right, so if there's two forces in the downwards direction, and one of them is gravity, then what can we say about the total force acting on the ball

5. Oct 11, 2012

### chewchun

Yes,but won"t it be that total downward force is larger than 9.81ms-2?
But Option D seems to imply that it is accelerating upward.

6. Oct 11, 2012

### SHISHKABOB

7. Oct 11, 2012

### chewchun

So option D is saying,When it is traveling upwards,net force/acceleration is acting downwards but it's magnitude is larger than 9.81 due to presence of air resistance???

8. Oct 11, 2012

### SHISHKABOB

that's what D appears to be saying, is that what you think is happening?