How to do the Radium Question (i hope im right) (1 Viewer)

[sharp_pencil]

a)
Propose A=10

5=10e^-1600k

0.5=e^-1600k

-1600k= ln 0.5

k= ln0.5/-1600

b)

For safe level q = 1 a =3 (since its 3X Q being the safe level)

1=3e^(ln0.5/-1600)t

1/3 = e^(ln0.5/-1600)t

(ln0.5/-1600)t=ln 1/3

t= (ln 1/3) / (ln0.5/-1600)

which = 2535.94 yrs

= 2536years

if im wrong please correct me this is how i approached the questions..

btw how to do questioin 9 B all of them..

because u cant just calculate the price to go from P--->R then R--->S

because from Q----R is above the shore hence different cost maybe i couldn't think or concentrate any help would be appreciated

 

[mitchwong650]

This is correct. and in 9)b

i) P to R is just 5 * 1000 = 5000
R to S is 3 * 2600 = 7800

Total =12800

Q and R are ON the shore line, not above

ii) P to S, find hypotenuse which is Root 34

root 34 * 2600 =

iii) not hard, just find PQ and QS using pythagoras' theorem


iv) minimise it by deriving C,

it's been posted in many places that x=1.25 thus min cost is 12200

v) replace 2.6 with 1.1 in part iv)

hope that helps

 

[fayad158]

fuck yesss! i was bit worried bout 6b but i did exactly the same thingggggg

 

[kushna]

Instead of subbing in values for A and Q you can make Q=A/2 (as the question tells you Q is half of A after 1600 years). Then you get 1/2 anyway by diving both sides by A, so I got the same answer as you. Similarly, with ii), you can make Q=A/3 to get 1/3. I also got the same answer here (I think).

I have no fucking clue why people thought this question (and the rollercoaster question) was difficult, I found it extremely easy.

 

[fayad158]

lol i got them both correct i just became uncertain when everyone starting talking about the rollercoaster question and about how hard it was

 

[lizajane91]

yay i got this one! i actually thought it was one of the easier questions

 

[alphaqup]

This is correct. and in 9)b

i) P to R is just 5 * 1000 = 5000
R to S is 3 * 2600 = 7800

Total =12800

Q and R are ON the shore line, not above

ii) P to S, find hypotenuse which is Root 34

root 34 * 2600 =

iii) not hard, just find PQ and QS using pythagoras' theorem


iv) minimise it by deriving C,

it's been posted in many places that x=1.25 thus min cost is 12200

v) replace 2.6 with 1.1 in part iv)

hope that helps

In Q9. B part iv if you replace the 2.6 with 1.1 you will end up with x being greater 5 which but 0 < x < 5 therefore shortest path is P to S directly

 

[HailSatan]

Awesome, I got this right. That was the exact same value I used to sub in lol

 

[MetroMattums]

Yeah you're right.

Except it was unnecessary to substitute A = 10. It cancels with A/2, if you read the question.

 

[mitchwong650]

In Q9. B part iv if you replace the 2.6 with 1.1 you will end up with x being greater 5 which but 0 < x < 5 therefore shortest path is P to S directly

my bad, forgot to write that in, had to go eat

thanks for that