Physics please help!!! (1 Viewer)

kashkow

Active Member
Joined
Oct 29, 2015
Messages
177
Location
Right here.
Gender
Male
HSC
2016
Hi guys,

Can someone explain why the answer is C? Is the HSC answers wrong or am I just missing something of the slingshot effect? :spin:

physics help.PNG

Like I thought velocity changes but speed of the satellite remains constant in this process... (This q is a multiple choice q from http://mcq.bostes.nsw.edu.au/)

Although now that I think about it, I realise that the speed doesn't change relative to the planet but picks up velocity relative to everything else... Is this why the "speed" changes?

If someone could explain that would be great!

Thanks!
 
Last edited:

trecex1

Active Member
Joined
Mar 19, 2016
Messages
196
Gender
Male
HSC
2017
What do you mean the velocity changes but the speed remains constant?
Assuming these are all relative to the sun, a space probe's velocity increases from the transfer of kinetic energy and momentum from the planet, its direction also changes as it's 'curving' around the planet. Velocity is just speed with a direction, and speed increases while it's direction also changes so it would be C.
 

kashkow

Active Member
Joined
Oct 29, 2015
Messages
177
Location
Right here.
Gender
Male
HSC
2016
Well, relative to the planet, the speed does not change. ie. It will approach the planet at x, swing around and leave the planet at x speed in a new direction (thus speed is same but velocity changes). It is only because the planet is moving relative to the sun that the probe's speed increases relative to the SUN. Unless I'm mistaken and speed relative to the planet also changes, which I don't think it does?
 

trecex1

Active Member
Joined
Mar 19, 2016
Messages
196
Gender
Male
HSC
2017
Well, relative to the planet, the speed does not change. ie. It will approach the planet at x, swing around and leave the planet at x speed in a new direction (thus speed is same but velocity changes). It is only because the planet is moving relative to the sun that the probe's speed increases relative to the SUN. Unless I'm mistaken and speed relative to the planet also changes, which I don't think it does?
It doesn't say relative to the planet, if the planet is used as the frame of reference then the slingshot effect won't appear to have any effect since it doesn't increase the speed.
That's why the speed and direction both change.
 

kashkow

Active Member
Joined
Oct 29, 2015
Messages
177
Location
Right here.
Gender
Male
HSC
2016
It doesn't say relative to the planet, if the planet is used as the frame of reference then the slingshot effect won't appear to have any effect since it doesn't increase the speed.
That's why the speed and direction both change.
Yeah ok, that is what I was thinking... I feel like this question is vague for not indicating the reference frame; because the answer depends on what reference frame is used (especially since B is there). Is it expected in HSC physics to use the reference point as the sun or some other point in space (besides the planet) when dealing with questions like these? Or is it just worded badly?

I thought it might've been a trick question by making most people think C (since most people think, "slingshot effect, changed velocity") but the use of "speed" rather than "velocity" made me think the answer was B (I was also thinking that slingshot effect only changes direction; forgot relative to the sun it increases actual velocity/speed as well).

Anyway, thanks for your help. I just wanted to make sure there were no holes in my understanding :)
 

DatAtarLyfe

Booty Connoisseur
Joined
Mar 10, 2015
Messages
1,805
Gender
Female
HSC
2016
Generally slingshot questions are asked from the frame of the sun, unless stated otherwise.
So yeh, speed and direction changes
 

Users Who Are Viewing This Thread (Users: 0, Guests: 1)

Top