Y_Shun SG wtf after the previous help., i can draw diagrams but it seems like its always wrong =[ i want to know how coem for this qtn i am wrong...(i cannot find the ans) An aircraft is flying due south at 350km/h. The wind is blowing at 70km/h from the direction x°, where x° is acute. Given that the pilot is steering the aircraft in the direction 170°, find value of x the speed of aircraft in still air. If you caculate, 70/sin 10 = 350/sin B B = 60.25485843 Then, if you use 180 - 60 - 10 = 119 and you can find x. but from the diagram you can already see that X is defintely less than 119 !!! how come ar??!?!?!
eagle SG 1. It is already said that x is acute 2. Your diagram is half correct. Do take note of how triangular sum of forces work
Y_Shun SG wrong mehs. we learn VA/W + VW = VA x is acute ma, hence in the diagram its oso acute rite?
nightzip SG heheh, do you know that sin 60.29... is the same as sin 119.... = same answer? because when you invert sin b to get b, it can be at any sector.
eagle SG It seems like you are correct... But I need to clarfiy something... Why is it that the question says that x is acute? Where did this question come from? And what is the given answer?
nightzip SG same same, the reason I think is that when he invert sine to get angle B, the default for calculator is always the smaller angle, which is not the answer.
nightzip SG the wind line is supposed to give an obtuse angle lah...if you draw it according to dimensions, you will see that the angle is >90. 350 line is very long. Because sine when drawn on graph is at the positive curve from 0 deg to 180deg, of which between 0-180, there is 2 identical values for sine theta.
Y_Shun SG so supposingly, 70/sin 10 = 350/sin B B = 60.25485843; 119.7451417 but in this case how do we know which value to reject and when do we need to find the larger value?
nightzip SG Anyway, if you draw a perpendicular line from the intersection of the two blue lines to the black line to form a 90deg angle at the black line side, part of the angle for angle B is already 80deg.
Y_Shun SG so we need to calculate the 2 values ar... so for sine rule that we are using, we must always have 180 - basic angle?
Y_Shun SG whats what i have on my paper, i lazy to draw out on the diagram...hence thats why i come here posting it.
eagle SG because sin x = sin (180 - x) It depends on the question whether it is acute or obtuse, or as what nightzip has said.
nightzip SG This one I let Eagle answer. My own way is that I just observe the diagram and logic can deduce already. The reason why the question deliberately want to tell you that angle is acute is so that you will not get wrong value.
