Relative Velocity

lpx88 SG

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Chey -.- I tot u inhuman sia..last part also no kick Laughing

eagle SG

now then I check your answer

you got the correct answer but the method is wrong

swimming at angle teta does not mean swimming directly to c

furthermore, teta should be wrt to the horizontal

means

Rindy aims at a location behind B and starts swimming towards there. That's why he will end up at C instead of D

eagle SG

btw, which year is this question from? I assume it is an O level question

My method uses the R-formula, but I think it is already out of syllabus

I try and see got any other method

Y_Shun SG

not sure if its ‘adapted from o lvl’, its from a school exam prelim paper…>_>

lpx88 SG

Which sch?

Y_Shun SG

presbyterian sec

eagle SG

ok I got a method which you will have learned before

but u all try a bit first hor

Small Hint:

^tamago^ SG

i thought of that but i have weird vectors. i actually went there one round before concluding to try test atan(0.8). i go try again. Confused

lpx88 SG

Thx eagle.. I got the answer...ive not drawn such a velocity diagram before though, which probably explains y i cant get the ans Laughing Embarassed

^tamago^ SG

50 / sqrt(4 + (1.2 * 1.2) + (4.8 * cos((53.1 / 180) * pi))) = 17.33s Sad

lpx88 SG

Using sine rule, u shud get that big angle red as a right angle.

With that get angle in green..180 degrees - 90-36.9 = 53.1

Cause right angle triangle, can use Pythagoras theorem to get velocity the guy travelling at... sqrt (2 sqaure - 1.2 sqaure)

Distance is 50m from another Pythagoras theorem as well. Sqrt (40 square + 30 square)

Dist/velocity=31.3 sec(Rounded off)

eagle SG

I hope everyone knows why it is 36.9 degrees

then:
find alpha using sine rule (ans: 90 degrees)
then you can find teta

eagle SG

this part can use my earlier solution

^tamago^ SG

50 / sqrt(4 + (1.2 * 1.2) - (4.8 cos((53.1 / 180) * pi))) = 31.2623186

walao waste time. could have solved it in much earlier. bang my own balls. Laughing

^tamago^ SG

thanks all for the help. Laughing it's a honest arithmetic mistake. Sad Embarassed

Y_Shun SG

i dun get it =x.

^tamago^ SG

AC is 50m. Find the resultant velocity (in green) from A to C through the diagram and use AC divide by the speed.

Y_Shun SG

How come AC is 50?

I thought its BD?

seotiblizzard SG

Rolling Eyes

^tamago^ SG

ABC is a right-angled triangle.
AB=30m
BC=40m
So hyp AC=50m

Mr. Green

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