A few questions... (1 Viewer)

[Premus]

1. HSC 2003 Multiple choice q14

2. just want to confirm this regarding circuits

In series : the voltages of the components should add up to give the main voltage?
and the currents remain the same for all the components right? Also, what happens to the resistances?

In parallel : the voltages across EACH component should be equal to the main? and the currents split up according to the voltages? what abt the resistances?

i think there are formulas for the resistances for both series and parallel?

3. i know this question has been asked previously, but different people say different things..... so i would like to confirm it. its from the CSSA 2004

A rocket of initial mass 2000 tonnes, produces a constant thrust of 8 * 10^7 N during lift off by expelling 1500kg of exhause gas per second. calculate the net force acting on an 85kg astronaut 30 s after liftoff.

Thank you very much!

 

[pc_wizz]

1) i got D

because when e/m radiation travels through glass the speed is different, thus causing the spark length to shorten ... i think ... tell me if wrong

 

[Jase]

1. Is the answer D?

2. Yes and yes. Resistance is the same thing. Current is vice versa.

let a b and c be the voltages, resistances and current in each case.
Resistance and p.d.:
Series: Total= a + b + c
Parrallel: 1/total = 1/a + 1/b + 1/c

Current:
Series: 1/total = 1/a + 1/b + 1/c
parallel: total = a + b + c


3. Use this and you can't go wrong. write down-> a = NetForce/mass. and then ask, what is the NET force... So first you find how much mass is left. 2000x10^3 - 1500x30

then a = (T - mg)/m
= (8*10^7 - totalmass*9.8)/totalmass
= 31.13 ms^-2

EDIT: woops i thought i said find the acceleration...
in that case,
netF = seatupwards - weightforce
Net force = 31.13*85 - 85*9.8
= 1813.05N

 

[pc_wizz]

3) Calculation:

8 x 10^7 N is the resultant force

since F = m.a, after 30s:

m(rocket) = (2000x10^3) - (1500x30) kg
= 1955000 kg
= 1.96 x 10^6 kg

:. acceleration of rocket = F/m

:. a = (8 x 10^7)/(1.95 x 10^6) m/s^2


For the 85kg astronaut:

F = (85)[(8 x 10^7)/(1.95 x 10^6)]
= 3478 N


Cheers

 

[pc_wizz]

1. Is the answer D?

2. Yes and yes. Resistance is the same thing. Current is vice versa.

let a b and c be the voltages, resistances and current in each case.
Resistance and p.d.:
Series: Total= a + b + c
Parrallel: 1/total = 1/a + 1/b + 1/c

Current:
Series: 1/total = 1/a + 1/b + 1/c
parallel: total = a + b + c


3. Use this and you can't go wrong. write down-> a = NetForce/mass. and then ask, what is the NET force... So first you find how much mass is left. 2000x10^3 - 1500x30

then a = (T - mg)/m
= (8*10^7 - totalmass*9.8)/totalmass
= 31.13 ms^-2

EDIT: woops i thought i said find the acceleration...
in that case,
netF = seatupwards - weightforce
Net force = 31.13*85 - 85*9.8
= 1813.05N

hmm u sure? lol

i wrote the solutions from my teacher =/

 

[Jase]

Then i think you're teacher's wrong.. What happened to gravity?

I'm not too sure about my calculations.. but im pretty sure Net force means you have to take into account weight force downwards as well.

 

[senso]

1. Is the answer D?

yes the answer is D

 

[Steven12]

i got 3475newton as well

 

[mojako]

Then i think you're teacher's wrong.. What happened to gravity?

I'm not too sure about my calculations.. but im pretty sure Net force means you have to take into account weight force downwards as well.

u've got my support
the support from a wonderful little cat on the left

teacher isnt always right......

 

[CrashOveride]

60Co27 ----> ____ + Ni
How do you do these when like the atomic mass of Ni is not a nice integer?

 

[Jase]

That's impossible, it has to be 60.. or at least very very close to 60.

wait this is beta decay right? not some kind of advanced phenomenon im not aware of.