Understanding the Motion of a Skydiver During Descent | Newton's Laws

[robb_]

Why do you state for phase D gravity and weight?

 

[imy786]

ok, just gravity...

 

[imy786]

well weight= mg,
well overall the force is weight
as F=ma,
w= mg

 

[robb_]

I am not sure what you mean by overall force. If you mean net force, then the statement is wrong, as there is still air drag to add into the net force. Remember net force means add all the forces up and that (those together) equals m*a.
I don't like the term weight, but that is just me. Weight and the force of gravity are the same here.

 

[imy786]

phase A= skydiver jumps out of plane traveling at speed , acceleatating
phase B= traveling at terminal velocity , a=0
phase C = opens parachute , skydiver decelaretes to new terminal velocity.
drag and air resistance are the same. The chute changes the profile of the falling object. The shape of the object changes, so the drag force will change as well.

phase D= skydiver continues at this speed till reaches ground

phase C: drag and air resistance are the same. The chute changes the profile of the falling object. The shape of the object changes, so the drag force will change as well.

During the entire fall, there are only two vertical forces, gravity and the drag force. The drag depends upon several aspects of the falling object.

phase A and B:
downward force- gravity,
upward force- air resistance

phase C:
downward force-gravity
upwward force= drag and air resistance

phase D:
downward force=gravity
upward force=no upward force when reached ground

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is this k?

 

[robb_]

I think you are misunderstanding some fundamental aspects of basic dynamics here for you to repeat the statement that phase D has only one force. If there is only one force, the object accelerates.
I am not sure that I am helping here. I think you should study your text a bit more.

 

[imy786]

Robb i do understand
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if he has reached the ground the forces are balanced.

but surely gravity is still acting downwards for him to stay on the ground, otherwise if there was no gravity then he would fly up.

so if there is gravity downwards, there has to be equal and opposite force upwards for him to be there on the ground with no motion

 

[robb_]

You are unclear on the last phase then, as I have stated previously. Is the last portion, where the chute is open and the person is in the air at v = v_t or is the last phase wehn the person is on the ground? In any case, both situations have more than one force to account for. (And to be sure, let us skip the portion of the motion when the person just hits the ground until he is at rest w.r.t the ground)
"phase D:
downward force=gravity
upward force=no upward force when reached ground"
This is incorrect.

 

[imy786]

phase D:
downward force=gravity
upward force= upward force when reached ground"

what is the upward foce called that keeps the person stable and stationary on ground?
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[robb_]

Normal force.

 

[imy786]

thanks Rob,
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with your help, and my answer to the quesiton,
what mark out of 100 would u give for this quesiton.

and what else i can do to improve it

 

[robb_]

Sorry, can't help you there.

 

[imy786]

lol,,,,,,,,y not Robb?

 

[imy786]

youv done so much for me...answer to the question...? WOULDNT even be givng me the answer..to the CALCULATIOn question

 

[imy786]

well is there anymore improvement or mistakes in the final answer?

 

[robb_]

If you have any more specific physics questions, I can answer those. Subjective questions I will not get into.

 

[imy786]

i think most of this quesitons is done- just this left-

describe his motion using Newton’s laws and
define the frame of reference that you are using to describe the motion
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Newton’s second law tells us that if a body has an acceleration g, then that body must be subject to a force, F = mg. This force, the gravitational pull on the body due to the Earth, is called the weight of the body.

 

[imy786]

is this correct??

 

[imy786]

can someone please help me on the last part of this quesiton-

describe his motion using Newton’s laws and
define the frame of reference that you are using to describe the motion
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Newton’s second law tells us that if a body has an acceleration g, then that body must be subject to a force, F = mg. This force, the gravitational pull on the body due to the Earth, is called the weight of the body.

What will his refrence point be?

need help

 

[imy786]

can anyone tell me if my last answer is correct?

 

[imy786]

describe his motion using Newton’s laws and
define the frame of reference that you are using to describe the motion...

what will be the frame of refrence?

 

[imy786]

i need hint and advie on this..describe his motion using Newton’s laws and
define the frame of reference that you are using to describe the motion

how would i describe the divers motion using Newtons law

 

[imy786]

these 2 parts i need help for this quesiton

-define the frame of refrence that you are using to describe his motion

-describe his motion using Newtons laws

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this is my final answer

Phase A= skydiver jumps out of plane traveling at speed, accelerating
phase B= traveling at terminal velocity, a=0
phase C = opens parachute; skydiver decelerates to new terminal velocity.
Drag and air resistance are the same. The chute changes the profile of the falling object. The shape of the object changes, so the drag force will change as well.
Phase D= skydiver continues at this speed till reaches ground

phase C: drag and air resistance are the same. The chute changes the profile of the falling object. The shape of the object changes, so the drag force will change as well.

During the entire fall, there are only two vertical forces, gravity and the drag force. The drag depends upon several aspects of the falling object.

Phase A and B:
downward force- gravity,
upward force- air resistance

phase C:
downward force-gravity
upward force= drag and air resistance