Question

1. Physicists use the phrase "free fall" to mean any period of time when an object is moving only under the force of gravity. During which parts of the ball's motion was the ball in free fall?

a) Only on the way up

b) Only on the way down

c) Only at the top

d) For half of the way up and all of the way down

e) The entire time

2. Three students are discussing their answers to the previous question.

Student 1: The ball has the acceleration from the throw on the way up. And when that runs out at the top it turns around and gravity pulls it down. So it's only in free fall for last part of the movement up and all of the movement down.

Student 2: I don’t know. I don’t think the throw matters after the person’s hand stops touching the ball. I think maybe it’s gravity pushing it up and then once it’s at the top gravity pulls it back down. So I think it's only free fall for the way down.

Student 3: I think gravity pulls it down the whole time. I don’t think the acceleration ever points up. So I think it's free fall the whole time.

Which student do you agree with?

a) Student 1

b) Student 2

c) Student 3

3. What kinematic equation should we use to find how long the object is in the air?

4. Can we solve for ∆t by moving all the terms with ∆t to one side and factoring?

Answer 1

1. As the ball's motion is under the influence of gravity for the entire journey , it's called free fall.

Hence Answer is option 'e'

2. As per the above explanation, student 3 is correct at his explanation that Acceleration is always in the downward direction

3. As we know, the total displacement (S) = 0

For the ball to come back to its initial position again,

Equation used = S = ut +1/2 at 2

Where u = initial velocity of projection

a= -g ( Acceleration due to gravity )

t = time

4. Here

ut= 1/2 gt^2

t =2u/g