# How does force change momentum?

#### Kamal

Let's say we are in outer space.Suppose I have 2 metallic balls A and B with initial velocity 0 and same mass M and a baseball bat.Let's say I hit the ball A with force F and ball B with F' in such a way that F>F'.Ball A attain final velocity V in time T and ball B attain final velocity V' in time T'.Let's say D is distance travelled by A in time T and D' is distance travelled by B in time T'.I know that V >V'.Please say whether T>T' or vice versa and D>D' or vice versa.

Related Classical Physics News on Phys.org

#### phinds

Gold Member
Let's say we are in outer space.Suppose I have 2 metallic balls A and B with initial velocity 0 and same mass M and a baseball bat.Let's say I hit the ball A with force F and ball B with F' in such a way that F>F'.Ball A attain final velocity V in time T and ball B attain final velocity V' in time T'.Let's say D is distance travelled by A in time T and D' is distance travelled by B in time T'.I know that V >V'.Please say whether T>T' or vice versa and D>D' or vice versa.
What do YOU think, and why?

@Kamal I see that you are new to the forum so you may be under the mistaken impression that this is a Q&A forum where you just ask a question and get the answer. It is not. We expect you to give your own answers and explain your own thought process and then we can help if you have gone wrong.

#### russ_watters

Mentor
Thread moved to classical physics.

• Kamalesh

#### Dale

Mentor
Let's say I hit the ball A with force F and ball B with F' in such a way that F>F'.Ball A attain final velocity V in time T and ball B attain final velocity V' in time T'. ... I know that V >V'.
Actually, we do not know that V>V' because we are not given any information about T or T'.

#### Kamalesh

Actually, we do not know that V>V' because we are not given any information about T or T'.
Since F>F' and initial velocity is zero we can say V>V' because greater the force greater will be the energy transfered greater the energy transfered greater will be the final velocity.

#### Dale

Mentor
Since F>F' and initial velocity is zero we can say V>V' because greater the force greater will be the energy transfered greater the energy transfered greater will be the final velocity.
This is not correct. What will happen if F = 10 N and F' = 5 N (F>F') and if T = 1 s and T' = 10 s?

• Delta2

#### Delta2

Homework Helper
Gold Member
The "logical path" that I consider to take on this, is first to make the logical assumption that the times T,T' will be both small and approximately equal (since we hit the balls with a baseball bat). And since F>F' the momentum transfer to the balls is FT and F'T'=F'T with FT>F'T, and since balls have equal mass, it follows that V>V'.

#### Dale

Mentor
first to make the logical assumption that the times T,T' will be both small and approximately equal (since we hit the balls with a baseball bat)
I agree that is a logical and a good assumption generally, but unfortunately the problem is that in the end the OP wants to know:
whether T>T' or vice versa and D>D' or vice versa.
So by making that assumption you are directly assuming part of the desired conclusion. That may not be a problem for the OP, but I think they need to be explicit.

If I were to recommend additional assumptions I would make the assumption that the two balls could be modeled as springs with identical modulus of elasticity and the bat could be modeled as rigid.

#### gmax137

I'm not sure exactly what the OP is after. "Hit the ball A with force F" is kind of ambiguous; it is certainly different than "push with force F for T seconds" or "push with force F for D meters."

Hitting with a bat implies an interest in Impulse not Force.

Until this is clarified the discussion has little meaning.

• nasu and sophiecentaur

#### phinds

Gold Member
Until this is clarified the discussion has little meaning.
Yeah, that is SUCH a problem on this forum. People just pile on even after an OP has been asked to clarify something or explain HIS though processes but has made zero response, as in this case. I've been noticing that more and more lately but it has always been the case at least to some extent.

### Want to reply to this thread?

"How does force change momentum?"

### Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving