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Help with this question please.
nickglyn:
Hey, so I'm 100% confused as how to do part part ii and iii. What the hell do they mean by low tide?
Much appreciated!
jakesilove:
--- Quote from: nickglyn on October 17, 2016, 04:13:42 pm ---Hey, so I'm 100% confused as how to do part part ii and iii. What the hell do they mean by low tide?
Much appreciated!
--- End quote ---
Hey! Low tide is going to be the minimum height of the water. We know that the minimum value of sin(anything) is -1, therefore the minimum height will be 1+0.7(-1)=0.3m
For the second part, you just need to solve when the height is 1.35. You'll get two values for the time, and the solution will be between those two times! Draw yourself a graph, and put a dotted line at 1.35m. You'll see the intercepts clearly; you're looking for the portion of the graph above that line.
Let me know if you want a proper worked solution, or if this is enough info!
nickglyn:
I tried doing it your way but I wasn't sure how to get the intercepts :/ I had a look at the sample answers and I don't get what they really mean, can you help explain how you did it your way and how they did it?
jamonwindeyer:
--- Quote from: nickglyn on October 17, 2016, 04:43:01 pm ---I tried doing it your way but I wasn't sure how to get the intercepts :/ I had a look at the sample answers and I don't get what they really mean, can you help explain how you did it your way and how they did it?
--- End quote ---
I'll let Jake explain his way, but what they've set up in your image is a simple inequality. The LHS is the height, and the RHS is the requirement of 1.35 metres. They are solving for values of t which gives a value of height that is enough for the condition to be satisfied! Notice how from second to third line, they give the angle range that puts the sine ratio to a value of one half or greater :)
jakesilove:
--- Quote from: nickglyn on October 17, 2016, 04:43:01 pm ---I tried doing it your way but I wasn't sure how to get the intercepts :/ I had a look at the sample answers and I don't get what they really mean, can you help explain how you did it your way and how they did it?
--- End quote ---
My way is exactly the same as theirs, except instead of an inequality, I would just set h=1.35. Then I would solve for values of t, and decide whether the answer was WITHIN the two values for t, or OUTSIDE of the two values for t (by testing a point between, and a point outside). They are literally the same methods :) Just set up the equation, set h=1.35m, and solve for t
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