VCE Physics Question Thread!

[Maz]

hey
can someone please help me with this question?
A canoeist can paddle a kayak for short bursts at a speed of 2.7 ms^-1 in still water. he wants to cross a stream in which a 2ms^-1 current flows. At what angle to the current must he point his canoe if he wants to land on the bank directly opposite where he started.?

Thankyou so much in advance 

[bedigursimran]

Hey guys. Can anyone help me with this motion question? Thanks

[Syndicate]

hey
can someone please help me with this question?
A canoeist can paddle a kayak for short bursts at a speed of 2.7 ms^-1 in still water. he wants to cross a stream in which a 2ms^-1 current flows. At what angle to the current must he point his canoe if he wants to land on the bank directly opposite where he started.?

Thankyou so much in advance 

Is it all the information given? I believe the question is missing some valuable information (how far is the bank?)

[Elisha913]

Have any of you guys done a data analysis sac for electronics??? I have mine on Wednesday and I literally don't know what to expect, are there any practice ones online?

[YellowTongue]

What actually is a data analysis SAC? I've never done one before...

[Elisha913]

What actually is a data analysis SAC? I've never done one before...

I have mine today so I'll tell you later :')

[Maz]

hey
I'm doing circular motion...could someone please help me with this question?

A pilot flies her aeroplane in a vertical loop of diameter 1.6km
Ignoreing air resistance, what is the speed of the aeroplane as it emerges from the bottom of the loop?

i'd really appreciate the help
thankyou so much in advance 

[JI2015]

G.P.E.=K.E.
mgh=0.5mv^2
gh=0.5v^2

v=(2gh)^0.5

In this case: v=(2*9.8*1.6*1000)^0.5= 177m/s

[Maz]

thankyou so much 

could you please possibly help me with another?
An aeroplane flies in a vertical loop of radius 650m. at the top of the loop the pilot experiences a downward reaction force, from her seat equal to one fifth of her weight. Estimate the aeroplane's speed at this instant.

thankyou 

[JI2015]

On the pilot:

The Fnet=W+R= mg+1/5(mg)=6/5(mg)

Fnet=F(centripetal)=mv^2/r

so 1.2mg=mv^2/r 1.2gr=v^2 Hence v=(1.2gr)^0.5

Sub the known values into v=(1.2gr)^0.5, we get v=(1.2*9.8*650)^0.5= 87m/s

[HopefulLawStudent]

I have two urgent questions. SAC is on Monday... Please help. Will be forever grateful.

1. In the study design, in the photonics and electronics section, they say we need to calculate the effective resistance for circuits comprising of unloaded voltage dividers. What's an unloaded voltage divider?

2. The study design says we need to know stuff re:"energy transfers and transformations in opto-electric devices". Is that that stuff about how electrical energy is transferred to thermal/light/whatever energy?

[Swagadaktal]

I have two urgent questions. SAC is on Monday... Please help. Will be forever grateful.

1. In the study design, in the photonics and electronics section, they say we need to calculate the effective resistance for circuits comprising of unloaded voltage dividers. What's an unloaded voltage divider?

2. The study design says we need to know stuff re:"energy transfers and transformations in opto-electric devices". Is that that stuff about how electrical energy is transferred to thermal/light/whatever energy?

1) A loaded voltage divider is where the resistance of a load in parallel is far too great for it to impact the effective resistance, so I'm going to assume that unloaded is an object that is attached in parallel where the resistance is not too high so that it actually impacts the total effective resistance in that parallel section of the circuit (hope this makes sense)
2) Yeah energy transfer: Using source-> input  transducer -> modulator -> demodulator -> output transducer -- used in the transmission of a signal/data (such as audio)
Opto-electric devices specifically talks about LED's and LDRs, you could potentially be asked about the benefits of using an LED over an LDR in the process of transmission through modulation. (it's more immediate so the signal would be more accurate)

Hope this helps

[HopefulLawStudent]

Thanks Swag!

So basically for the first point, we just need to know circuits like this one:



Or circuits that can be simplified into something like that?

Basically stuff that we can use the V_out = V_in (R₁/(R₁ + R₂)) formula for?

[Swagadaktal]

Thanks Swag!

So basically for the first point, we just need to know circuits like this one:

(Image removed from quote.)

Or circuits that can be simplified into something like that?

Basically stuff that we can use the V_out = V_in (R₁/(R₁ + R₂)) formula for?

OOPs wait a sec I think I go my definitions mixed.
Unloaded follows the laws of Vout = Vin*r1/r1+r2  with no potential for the effective resistance to be changed.

Loaded is where the resistance attached can either be too high for it to make an impact or it can change the effective resistance if its low enough - generally speaking though you can approach the questions the same way you'll just have to add in an extra step. I doubt they'd ask the differences between.

And yes that's a kind of circuit you'll encounter - your practice qs in book or practice sacs should have plenty of example circuits with voltage dividers

[HopefulLawStudent]

Gotcha. Thanks again!