# Thread: Ambiguous HSC space multiple choice

1. ## Ambiguous HSC space multiple choice

Screen Shot 2017-09-21 at 3.53.26 pm.png

This question is from 2005 HSC physics!
A space probe, P, is in a stable orbit around a small, distant planet. The probe fires a
forward-facing rocket that reduces its orbital speed by half.
Which of the following best illustrates the subsequent motion of the probe?

I can't understand why it is D!

Anyone know how to solve this?
Thanks!

2. ## Re: Ambiguous HSC space multiple choice

It is only reduced by half. That does not mean its gonna instantly hit the surface. It will slowly decay, and as it comes into contact with the atmosphere the friction upon the space probe will increase and it will then eventually hit the surface. I presume you went for C, this cannot be correct as the decay is too steep and swift.

3. ## Re: Ambiguous HSC space multiple choice

thanks green yoda, much appreciated!

4. ## Re: Ambiguous HSC space multiple choice

That is a very poor explanation, obviously aided by the fact that you know he answer that was marked correct is D.

There is no particular reason to discount C........"velocity only reduced by 1/2" is not an explanation....... since we do not know any other variables such as mass of planet, altitude/radius ratio ( since not a scale drawing......it might only be in a 100 km altitude orbiting a remarkably dense planet which would allow C)

The OP had the right idea....the question is ambiguous with no compelling physical reason to choose D other than it "looks" right......as I pointed out to BOS in 2005/ That particular paper was a stinker BTW

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