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How to do these questions? (2 Viewers)
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ExtremelyBoredUser
Bored Uni Student
Rough outline:
For (i), draw up a diagram of the mass, with the forces and take the resistive forces (going up the slope) as negative and the weight force parallel to the mass (mgsintheta) as positive:
So net force would be mgsinx - 2v - 2v^2
and sub m =5, theta = 60 degrees and you'll get the required answer.
(ii)
For constant speed, a = dv/dt (rate of change of velocity) = 0 i.e net force = 0 as f = ma:
So you'll get a quadratic in (i) and use the quad formula to solve for v.
For a guide, times equation inn (i) by 2 to get
Simplify or use your calculator and you should get 4.2 ms^-1.
so v = 4.2 ms^-1
Also the solutions should be on the HSC marking criteria on the website?
chilli 412
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in ext2 mechanics do we usually just assume v is always greater than zero even if velocity is in the downward direction?Rough outline:
View attachment 36664
For (i), draw up a diagram of the mass, with the forces and take the resistive forces (going up the slope) as negative and the weight force parallel to the mass (mgsintheta) as positive:
So net force would be mgsinx - 2v - 2v^2
and sub m =5, theta = 60 degrees and you'll get the required answer.
(ii)
For constant speed, a = dv/dt (rate of change of velocity) = 0 i.e net force = 0 as f = ma:
So you'll get a quadratic in (i) and use the quad formula to solve for v.
For a guide, times equation inn (i) by 2 to get
v > 0 so only consider positive
Simplify or use your calculator and you should get 4.2 ms^-1.
so v = 4.2 ms^-1
Also the solutions should be on the HSC marking criteria on the website?
mmmmmmmmaaaaaaa
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You can take the downwards direction as positive in that scenario
ExtremelyBoredUser
Bored Uni Student
Aight thanks bro. Any other advice/foresight for us tomorrow for the exam? Like any silly mistakes you made or some stuff you didn't know after the exam? Cheers
ExtremelyBoredUser
Bored Uni Student
I just stated in my solutions that I am taking downward as positive just because but I presume that they assume in that context that downward direction is positive given than the forces are considered "resistive".
Similar to the resisted motion in vertical Qs, taking down as positive when its falling etc...
Good luck for tomorrow as well man!
Keep your focus.
Ngl I feel like I was on autopilot most of my 4u hsc exam and didn't really have any aha moments. I think its because I wasn't focused. Don't know how to improve this one tbh.
Don't use trig sub if it isn't necessary e.g. 13b of 2021. Pay attention to the bounds if you need a hint. Your bounds after subbing should look nice.
Don't panic. If your working out looks terrible or you're just getting nowhere nice, then start again from the beginning.
Especially with algebra hell questions (e.g. q16 b 2021 which is actually quite straightforward if your algebra is correct. I have a friend who did better than me in 4u and made the exact same fumble as me. we both got 2/5 because our quadratics were not correct, so our discriminants were not correct etc.)
Finally, be confident in yourself.