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Chapter 2 Solution 78 Slides
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Step 3:
SOLVING THEPROBLEMS
The first thing we must do to solve thisproblem is find how long Wilfred and John willbe on the ride before Francis and Kieran getoff.
The first thing we must do to solve thisproblem is find how long Wilfred and John willbe on the ride before Francis and Kieran getoff.
We can do this by subtracting the time ofWilfred and John’s boarding of the ride fromthe time when Francis and Kieran get off.
The first thing we must do to solve thisproblem is find how long Wilfred and John willbe on the ride before Francis and Kieran getoff.
We can do this by subtracting the time ofWilfred and John’s boarding of the ride fromthe time when Francis and Kieran get off.
35Time that Francis and Kieran will get off
The first thing we must do to solve thisproblem is find how long Wilfred and John willbe on the ride before Francis and Kieran getoff.
We can do this by subtracting the time ofWilfred and John’s boarding of the ride fromthe time when Francis and Kieran get off.
35 - 21Time that Francis and Kieran will get off
How long ‘F’ and ‘K’ have been on the ride when ‘W’ and ‘J’ get on
The first thing we must do to solve thisproblem is find how long Wilfred and John willbe on the ride before Francis and Kieran getoff.
We can do this by subtracting the time ofWilfred and John’s boarding of the ride fromthe time when Francis and Kieran get off.
35 - 21 = 14Time that Francis and Kieran will get off
How long ‘F’ and ‘K’ have been on the ride when ‘W’ and ‘J’ get on
This tells us that Francis and Kieran will be getting off the ferris wheel in 14 minutes.
This tells us that Francis and Kieran will be getting off the ferris wheel in 14 minutes.
Therefore we can conclude that Wilfred and John will have been on the ferris wheel for 14 minutes.
Now that we know how long they have been onthe ride, we must find what height Wilfred and John are at when Francis and Kieran get off.
Now that we know how long they have been onthe ride, we must find what height Wilfred and John are at when Francis and Kieran get off.
We can do this by solving one of the equationsthat we derived a few minutes ago with t=14substituted into it.
Now that we know how long they have been onthe ride, we must find what height Wilfred and John are at when Francis and Kieran get off.
We can do this by solving one of the equationsthat we derived a few minutes ago with t=14substituted into it.
***I will be using both the sine and cosine equation for this part.***
Sine Equation
Sine Equation
H(t)=75sin((2π/35)(t-10.75))+76
The Original Equation:
Sine Equation
H(14)=75sin((2π/35)(14-10.75))+76
Substitute t=14 into the equation.
Sine Equation
H(14)=75sin((2π/35)3.25)+76
Simplify the brackets.
Sine Equation
H(14)=75sin(6.5π/35)+76
Simplify the brackets.
Sine Equation
H(14)=75(0.5509)+76
Calculate the sine of the value inside the brackets.[Accurate to 4 decimal places.]
Sine Equation
H(14)=41.3173+76
Simplify the equation.
Sine Equation
H(14)=117.3173
Simplify the equation.
Sine Equation
H=117.3173m
Cosine Equation
Cosine Equation
H(t)=-75cos((2π/35)(t-2.0))+76
The Original Equation:
Cosine Equation
H(14)=-75cos((2π/35)(14-2.0))+76
Substitute t=14 into the equation.
Cosine Equation
H(14)=-75cos((2π/35)12.0)+76
Simplify the brackets.
Cosine Equation
H(14)=-75cos(24.0π/35)+76
Simplify the brackets.
Cosine Equation
H(14)=-75(-0.5509)+76
Calculate the cosine of the value inside the brackets.[Accurate to 4 decimal places.]
Cosine Equation
H(14)=41.3173+76
Simplify the equation.
Cosine Equation
H(14)=117.3173
Simplify the equation.
Cosine Equation
H=117.3173m
This means that Wilfred and John were approximately 117 m off the ground when Francis and Kieran got off.
We have just answered the first part of the question.
We have just answered the first part of the question.
Now we must use this to answer the secondpart of the question:
We have just answered the first part of the question.
Now we must use this to answer the secondpart of the question:
How much longer will it be until they reach the same height again?
Some people might be confused by thisquestion, so lets take a look at it.
Some people might be confused by thisquestion, so lets take a look at it.
This is the graph that we constructed earlier.
Some people might be confused by thisquestion, so lets take a look at it.
The point on the graph is the point that we just found. (t=14)
Some people might be confused by thisquestion, so lets take a look at it.
The height of this point is 117m.
Some people might be confused by thisquestion, so lets take a look at it.
However, there is another point with a heightof 117m.
Some people might be confused by thisquestion, so lets take a look at it.
Therefore there is another time that theywill reach a height of 117m.
So, we are looking to find that second time which has a height of 117.3173m.
We can do this by making the equation equal to 117.3173m and solving it.
So, we are looking to find that second time which has a height of 117.3173m.
We can do this by making the equation equal to 117.3173m and solving it.
***This time I will only use the Sine equation and explain the difference between the two methods afterwards.***
Sine Equation
Sine Equation
H(t)=75sin((2π/35)(t-10.75))+76
The Original Equation:
Sine Equation
117.3173=75sin((2π/35)(t-10.75))+76
Substitute H(t)=117.3173 into the equation.
Sine Equation
117.3173=75sinØ+76
Let ((2π/35)(t-10.7))=Ø to make it a little easier to work with.
Sine Equation
41.3173=75sinØ
Simplify the equation.
Sine Equation
0.5509=sinØ
Simplify the equation.
Sine Equation
0.5834=Ø
Calculate the arc sine of 0.5509 [to four decimal places].
Sine Equation
Now we have an angle.
The measure of this angle is 0.5834 radians
Another thing we know about this angle is that it’s sine is positive.
WHY IS THIS HELPFUL???
Sine Equation
Well, when the sine of an angle is positive, it must either be in Quadrant 1 or 2.
This particular angle is in Quadrant 1.
HOW DO WE KNOW THIS???
Well, when the sine of an angle is positive, it must either be in Quadrant 1 or 2.
This particular angle is in Quadrant 1.
HOW DO WE KNOW THIS???
Sine Equation
QIQII
QIII QIV
!/2
0!
3!/2
2!
Here we have the Unit Circle.
Sine Equation
QIQII
QIII QIV
!/2
0!
3!/2
2!
The angle that separates Quadrants I and II is π/2.
[or 1.5707...]
Sine Equation
QIQII
QIII QIV
!/2
0!
3!/2
2!
0.5834 is much less than 1.5708 so it lies in Quadrant I.
Sine EquationThis means that to find the other point with the exact same sine value, it’s angle would have to be in Quadrant II.
Sine EquationThis means that to find the other point with the exact same sine value, it’s angle would have to be in Quadrant II.
To find this angle we simply subtract our angle from π (End of Quadrant II).
Sine EquationThis means that to find the other point with the exact same sine value, it’s angle would have to be in Quadrant II.
To find this angle we simply subtract our angle from π (End of Quadrant II).
π - Ø = Ø’
Sine Equation
2.5582=Ø’
Here we have our Quadrant II angle.
Sine Equation
sinØ=sinØ’
Now the two angles we have are related angles. This means their sine values are equivalent.
Sine Equation
Ø=Ø’
And if we take the arc sine of both sides and we see that:
Sine Equation
Ø=2.5582
Now we can continue where we left off.
Since...
Sine Equation
Ø= ((2π/35)(t-10.7))
...AND...
Sine Equation
2.5582= ((2π/35)(t-10.7))
...Then.
Sine Equation
14.25= (t-10.7)
Now just simplify.
Sine Equation
25= t
Now just simplify.
Sine Equation
t=25Cosine Equation
Cosine Equation
The Cosine equation works quite similarly to that of Sine.
Cosine Equation
The Cosine equation works quite similarly to that of Sine.
The equation is a little bit different as we saw earlier but that’s about all that applies to the first part of the procedure.
Cosine Equation
One of the major differences is when you simplify down to cosØ.
Cosine Equation
One of the major differences is when you simplify down to cosØ.
First of all, this value is negative which means the angle is either in Quadrant II or III.
Cosine Equation
One of the major differences is when you simplify down to cosØ.
First of all, this value is negative which means the angle is either in Quadrant II or III.
This one is in Quadrant II because it is 2.1542 which is less than π (3.1415), the end of Quadrant II.
Cosine Equation
This means Ø’ is in Quadrant III and we must subtract Ø (angle that passes Q I and into II) from the full circle (2π) so it passes through Q IV and into III.
Cosine Equation
This means Ø’ is in Quadrant III and we must subtract Ø (angle that passes Q I and into II) from the full circle (2π) so it passes through Q IV and into III.
After that, continue as shown in the Sine procedure until you get t=25 as your answer.
From here, we now can finish the problem off.
t=25 minutes
Since it takes 14 minutes to get from thestart to 117.3173 m the first time.
14
Since it takes 14 minutes to get from thestart to 117.3173 m the first time...
...And it takes 25 minutes to get from the startto 117.3173 m the second time...
14 - 25
...Then the time it takes to get from 117.3173 the first time to 117.3173 m the second timemust equal...
14 - 25 = ?
11 minutes
When Francis and Kieran get off “The Wheel”, Wilfred and John will be 117.3173 m from the ground.
It will take them 11 more minutes to get to that exact same height again.