I don't understand this conceptually.

[Lunasly]

---

Members don't see this ad.

Q. A 6 kg ball experiences a force due to gravity that is 2,000 times greater than the gravitational force experienced by a 3g ping-pong ball. Which of the following properties explains why they fell at the same rate?

A) Momentum
B) Weight
C) Inertia
D) Size

Answer: C (highlight)

Can someone explain to me why the answer is correct and why the others aren't?

 

[MedPR]

Q. A 6 kg ball experiences a force due to gravity that is 2,000 times greater than the gravitational force experienced by a 3g ping-pong ball. Which of the following properties explains why they fell at the same rate?

A) Momentum
B) Weight
C) Inertia
D) Size

Answer: C (highlight)

Can someone explain to me why the answer is correct and why the others aren't?

A. Momentum = m*v. If the force of gravity is greater for the heavier ball, then the velocity is greater since the acceleration is greater. This would make the heavier ball fall even faster than the lighter ball.

B. Weight = m*g. Same concept as above. If gravity and mass are greater, there's no way this explains why it falls at the same rate as a ligher ball.

C. Inertia is the tendency to stay at rest or stay in motion. Heavier objects are harder to move and harder to stop. The heavier object will want to stay in place more so than the lighter object, so it will move more slowly. This concept helps explain why something with a greater mass and force of gravity would move at the same speed as something with lesser mass and lesser force of gravity. Inertia "cancels out" gravity in a sense.

D. No information is given about the size of both balls.

 

[Lunasly]

Hmm. I got all of them except inertia. As far as I know, the definition of inertia is, as you stated, the tendency for an object to stay at rest or stay in motion (i.e. it resists changing from either state). However, what do you mean it "cancels" out gravity?

Are you saying that the heavier ball NEEDS a greater force of gravity to be set upon it in order to move it (or in this case for it to fall), while the smaller ball, being lighter, does not require as much of a force for it to fall. Therefore, the lighter object has a smaller inertia because it is easier to move from a state of rest to a state of motion. The heavier object has a greater inertia and thus it is more difficult for it to move from a state of rest to a state of motion. In the end, because F=mg, a greater force will be applied to the heavier object (2000 times greater in this case) allowing it to move at the same rate as the lighter object.

Did I say that correctly?

 

[Lunasly]

Bump

 

[pm1]

this scenario is true because it ignores air resistance, right?

 

[MedPR]

Yes, same speed because air resistance is ignored.

Hmm. I got all of them except inertia. As far as I know, the definition of inertia is, as you stated, the tendency for an object to stay at rest or stay in motion (i.e. it resists changing from either state). However, what do you mean it "cancels" out gravity?

Are you saying that the heavier ball NEEDS a greater force of gravity to be set upon it in order to move it (or in this case for it to fall), while the smaller ball, being lighter, does not require as much of a force for it to fall. Therefore, the lighter object has a smaller inertia because it is easier to move from a state of rest to a state of motion. The heavier object has a greater inertia and thus it is more difficult for it to move from a state of rest to a state of motion. In the end, because F=mg, a greater force will be applied to the heavier object (2000 times greater in this case) allowing it to move at the same rate as the lighter object.

Did I say that correctly?

Not really sure what you're trying to say, but I'll reword my initial post.

Of the answer choices, inertia is the only one that is completely dependent on the mass of the object and nothing else. You might (hopefully) have noticed that 6kg is 2000x greater than 3g.

 

[Lunasly]

I understand your explanation mathematically (inertia being directly proportional to mass), but I was just asking why? Does my explanation above describe the relation?