some questions from HSC 2004 !help! (1 Viewer)

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hey guys

i know this is kinda late..but hopefully someone is generous enough to help out..i'm sure it'll help out the rest too.
i posted an image for each question for easy referencing..and i hope you guyz can at least give me a guide, if not a general answer to the questions thanks ALOT!

Q18: are we meant to contradict? my answer (dunno if right or not) ended up saying that there IS a net force (being centrepital) and stated Newton's first law and basically reworded the rest of the statement.

Q20: what is A referring to? is that the earth cable? and what do you call the second one? um.. ceramic/glass insulator chains (disc shaped)?

Q27: The infamous basketball Q..umm i hav no idea..and how do i make 'appropriate calculations' using just '2.5sec'..

Q31 b) i) i know the quark composition for neutron..but what is the charge for a negative pion??? i never learnt that..so i have no idea of its quark composition..pls help

BIG THANKS..i hope the pictures show

 

[KFunk]

Q27: The infamous basketball Q..umm i hav no idea..and how do i make 'appropriate calculations' using just '2.5sec'..

Time of flight is 2.5s so when t=2.5 , y=0.

s = ut + 1/2.a.t² (s = y = 0)

(4.9)x(2.5)² = (2.5)x(u) therefore initial velocity u = 12.25 ms^-1. We also know that the time to reach max height is 1/2 the time of flight (1.25s) so we can calculate:

Max height = (12.25)x(1.25) - (4.9)x(1.25)²

= 7.6m

= the height of a two story building which Jordan (as cool as he is) cannot leap over.

 

[KFunk]

Q31 b) i) i know the quark composition for neutron..but what is the charge for a negative pion??? i never learnt that..so i have no idea of its quark composition..pls help

When you see (pi)^- it's like e^-. When you see a single minus like that it indicates that the particle has a charge of minus one (not simply that it has a negative charge). It'd be the same deal if you saw K^- which represents a Kaon particle with a charge of minus one. Given that charge then all you have to do is find a quark and an antiquark from the table which, when combined, add together to give a net charge of minus one. This would lead you to choose a down quark and an anti-up quark.

 

[helper]

18. You needed to have at least two supporting, so the comment about net force is fine. You would have to explain how come you knew this. You also had to use the centripetal force formula as you had to have mathematical support.
Type it in and I will tell you your mark.

20. Its a cable connected to Earth to protect the wires from a lightening strike.
insulators from support structure.

Straight from syllabus
– insulated from supporting structures
– protected from lightning strikes

 

[richz]

1st centripedal provided by tyre and road and work out centripedal and say theory is false.

q18 yes, earthing wire, prevents it getting damaged by lightning, it takes the lightning strike down to the ground, if u know wat i mean (kind of poorly worded)

 

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thanks guyz! for the speedy replies..its all making sense now!

and just needin one more help from 'helper' hehe .. here's my response to Q18...can u pls tell me how many marks i'll earn out of 4? just for fun..

i calculated centrepital force to be 2812.5 N (not sure how it'll help answer the Q)
According to Newton's 1st Law, a moving object will continue to move in a straight line unless acted upon by a net unbalanced force. Centrepital force, being 2812.5N act as the net force constantly changing the direction of the car. Thus, it follows a circular path (provided that it is balanced by the friction between road and tyre acting as the 'tension') but in contradiction to the statement provided, there is a net unbalanced force acting on the car.

how many marks is that?

 

[helper]

3 You have included a contradiction and wrong physics.
The reason for the calculation, is because the question said you had to include mathematical support.

The centripetal force is the net force which is supplied by the friction between the road and the tyre.

Other things, you could have included was the centripetal acceleration is towards the centre, centripetal force is towards the centre.
The speed is constant but the object is accelerating as it is changing direction.