Speed of ball vs Acceleration of the ball?

[Aaryan34532]

Homework Statement

Homework Equations

v = s/t
a = v/t

The Attempt at a Solution

My thinking was that through this small distance of air since velocity would increase due to the change in position changing at an increasing rate and thus since velocity is increasing then obviously acceleration would increase because a = v/t so a= 5/1 is 5m/s^2 and a=10/1 is 10m/s^2 then acceleration is increasing BUT

the markscheme says "A" speed of ball increases, acceleration decreases.. why does acceleration decrease?

 

[Delta2]

Think about all the forces that act on the ball. Especially think about the air drag force that acts on the ball. How does the air drag force changes as velocity increases?

 

[haruspex]

since velocity is increasing then obviously acceleration would increase

It is not even true, let alone obvious.
If acceleration is positive, what is happening to the velocity?

a = v/t so a= 5/1 is 5m/s^2 and a=10/1 is 10m/s^2

I do not understand your calculation. Please explain the situation you are considering and where these numbers come from.

why does acceleration decrease?

It is not in a vacuum.

 

[Aaryan34532]

@haruspex but wouldn't acceleration due to gravity at the start be greater than whatever drag forces existed? if acceleration is positive then velocity also must be positive.

 

[haruspex]

wouldn't acceleration due to gravity at the start be greater than whatever drag forces existed?

You cannot compare an acceleration to a force, they're different entities.
If you mean the force of gravity on the object, yes, it will be greater than the drag force, but how does that conflict with what I wrote?

if acceleration is positive then velocity also must be positive.

You have a basic misunderstanding of the relationship between velocity and acceleration.
It might help to start one level higher (thinking of differentiation as down and integration as up). I.e., think about displacement and velocity of a ball moving vertically.
I throw a ball up. Consider vertically up velocity and displacement from where I released it. At first, velocity is positive and decreasing, displacement is positive and increasing. After reaching maximum height, velocity is negative. Displacement is still positive but decreasing. Eventually, displacement and velocity are both negative.
Compare the positive/negative state of velocity (i.e. its sign) with that of displacement. Is knowing whether velocity is positive or negative enough to say whether the displacement is (or vice versa)? What about the relationship between the sign of the velocity and whether displacement is increasing or decreasing?

See if you can work out the relationship between the sign of the acceleration and what is happening with velocity.