Conservation of Momentum of a skydiver

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Discussion Overview

The discussion revolves around a physics problem involving the conservation of momentum as a skydiver drops from a glider. Participants explore the implications of external forces, particularly gravity, on the momentum of the glider and skydiver system, focusing on both horizontal and vertical momentum changes.

Discussion Character

  • Homework-related
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant expresses confusion about applying the conservation of momentum due to the influence of gravity as an external force on the system.
  • Another suggests to focus on the moment the skydiver drops, questioning how the momentum of the skydiver changes upon release.
  • A participant raises the idea that a change in momentum requires an impulse, questioning whether the skydiver's release generates a vertical impulse on the glider.
  • There is a discussion about whether the glider should gain vertical momentum in response to the skydiver's downward momentum, with some suggesting that gravity is the external force affecting the skydiver.
  • One participant concludes that the glider does not change velocity because there is no impulse acting on it, while another agrees with this assessment.
  • Participants discuss the potential for horizontal momentum changes and whether any impulse exists in that direction.

Areas of Agreement / Disagreement

There is no consensus on the impact of the skydiver's release on the glider's momentum, particularly regarding vertical and horizontal components. Some participants agree that the glider does not change velocity at the moment of release, while others question the implications of impulse and external forces.

Contextual Notes

The discussion includes assumptions about the effects of external forces and the definition of the system, which may not be fully resolved. The role of gravity and its influence on momentum conservation is a key point of contention.

James98765
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I reading a physics book on my own right now and I appear to be stuck. The problem is as follows:

A 10 m long glider with a mass of 680 kg (including the passengers) is gliding horizontally through the air at 30 m/s when a 60 kg skydiver drops out by realesing his grip on the glider. What is the glider's velocity just after the skydiver let's go?

The problem is dealing with the law of conservation of momentum. I feel like I understand the concept except this particular problem is confusing me. I have defined the system as glider + skydiver. The problem is that gravity is an external force acting on the system so momentum shouldn't be conserved. I don't quite know how to handle this. If anyone could help me that would be great. Thanks a lot!

-James
 
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Forget about gravity. Just worry about the "moment" when the skydiver drops. Hint: How does the momentum of the skydiver change when he let's go?
 
That's a good suggestion but I still don't understand one thing. Inorder for there to be a change in momentum their must be an impulse. Because the glider is supposed to gain vertical momentum, wouldn't there have to be a vertical impulse acting on the glider. I don't see how the skydiver letting go could cause I vertical impulse.
 
Why do you think the glider is supposed to gain vertical momentum?
 
It seems to make sense. If the skydiver is gaining downward vertical momentum shouldn't the glider have to gain upward vertical momentum due to the law of conservation of momentum. I guess that the momentum increase of the skydiver in the down direction is due to an external force (gravity). So that would mean that the glider wouldn't neccessarily have to accelerate upward. Does the glider change momentum in the horizontal direction? If so, where is the impulse in the horizontal direction causing the change?
 
James98765 said:
It seems to make sense. If the skydiver is gaining downward vertical momentum shouldn't the glider have to gain upward vertical momentum due to the law of conservation of momentum. I guess that the momentum increase of the skydiver in the down direction is due to an external force (gravity). So that would mean that the glider wouldn't neccessarily have to accelerate upward.
Exactly.
Does the glider change momentum in the horizontal direction? If so, where is the impulse in the horizontal direction causing the change?
What makes you think there's a change in horizontal momentum?
 
I think I am coming to the conclusion that the glider doesn't change velocity at all because there is no impulse acting on it. I can't check my answer because it isn't in the book but the conclusion seems valid.
 
James98765 said:
I think I am coming to the conclusion that the glider doesn't change velocity at all because there is no impulse acting on it.
You are correct. Neither glider nor skydiver change velocity at the instant he let's go.
 
Okay thanks a lot for your help! I think I fell for a trick question from my textbook. I wasn't expecting that. Thanks again! You lead me to a conclusion perfectly!

-James
 

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