Modelling with Trigonometric Functions (A Level only) (OCR A Level Maths: Pure)

A small spring is extended to its maximum length and released from rest.

The length of the spring, cm , at time seconds, where the angle is given in radians, is then modelled by the function

cos 

State one criticism of this model as time passes.

A dolphin is swimming such that it is diving in and out of the water at a constant speed. On each jump and dive the dolphin reaches a height of 2 m above sea level and a depth of 2 m below sea level.
Starting at sea level, the dolphin takes  seconds to jump out of the water, dive back in and return to sea level.  

Write down a model for the height, m, of the dolphin, relative to sea level, at time seconds, in the form sin  where are  constants to be found.

The path of a swing boat fairground ride that swings forwards and backwards is modelled as a semi-circle, radius cm, as shown in the diagram below.

Ground level is represented by the -axis and  represents the height of the boat above ground level.  The path of the boat is given by the formula

The boat’s initial position is at the point .

Find the height of the boat when it is m horizontally from its initial position.

When the boat is at a height of m, find its exact horizontal distance from the origin.

Given that the -coordinate of the boat is also given by

sin 

where  seconds is the time since the boat was released from its initial position, find the time it takes the boat to swing from one end of the ride to the other.

The height, m , of water in a reservoir is modelled by the function

where  is the time in hours after midnight.  and   are positive constants.

In terms of  and , write down the natural height of the water in the reservoir, as well as its maximum and minimum heights.

The maximum level of water is 3m higher than its natural level.

The level of water is three times higher at its maximum than at its minimum.

Find the maximum, minimum and natural water levels.

A Ferris wheel with  passenger “pods” is modelled as a circle with centre  and radius m.  A pod’s position can be determined by the angle, radians, which is measured anticlockwise from the positive -direction, as shown in the diagram below.

The coordinates of a pod, , are given by  , where  is a positive constant. Ground level is represented by the line with equation y=-60.

Write down the value of the constant .

The angle between each pod is   radians. Find the value of .

Find, to three significant figures, the angle for a passenger pod located at the point .

A lifejacket falls over the side of a boat from a height of m.
The height, m, of the lifejacket above or below sea level , at time  seconds after falling, is modelled by the equation cos  .

The lifejacket reaches its furthest point below sea level after 0.742 seconds.
Find the total distance it has fallen, giving your answer to three significant figures.

Write down the value of for the first three times the lifejacket is at sea level.

The number of daylight hours, , in the UK, during a day  days after the spring equinox (the day in spring when the number of daylight hours is 12), is modelled using the function

For how many days of the year does the model suggest that the number of daylight hours exceeds 15 hours? Give your answer as a whole number of days.

The alternating voltage, , in an electrical circuit,  seconds after it is switched on, is modelled by the function

Show that

can be written as

sin

where and .

After how many seconds does the voltage first equal -55 volts?

The length of a spring, cm , at time  seconds, after being released from rest, is modelled by the function

cos 

Describe what the constants and represent in terms of the length of the spring.

Given that the minimum length the spring can attain is cm and its maximum length is 30 cm, find the values of and .

A hovering helicopter moves up and down at a constant rate between the heights of 200 m and 220 m.  It takes the helicopter  seconds to move between these two heights.
Write down a model in the form cos for the height, m, of the helicopter at time  seconds, where are  constants to be found.
State the initial height of the helicopter suggested by your model.

The path of a swing boat fairground ride that swings forwards and backwards is modelled as a semi-circle, radius m, as shown in the diagram below.

At time  seconds, the -coordinate of the boat is modelled by the function

sin

and the height, m , of the boat above the ground, at time  seconds, is modelled by

Verify that the initial position of the boat is .

Find the position of the boat when it has swung through an angle of anticlockwise from the -axis, as shown in the diagram above. 
Find the time at which the boat first reaches this position.

The height, m, of water in a reservoir is modelled by the function

sin

where  is the time, in hours, after midnight.  and   are positive constants.

Given that the water level rises and falls through one and a half cycles in a 24 hour period, find the value of .

The height of water reaches its minimum of m just once per day.

The maximum height of water is m. Find the values of and .

The reservoir is only capable of holding water to a maximum height of m
Should the water level exceed this, an overflow reservoir is available.

During which times of day will the overflow reservoir be in use?
Give your answers to the nearest minute.

A Ferris wheel with  passenger “pods” is modelled as a circle with centre  and radius m.  A pod’s position can be determined by the angle  radians, which is measured anticlockwise from the positive -direction, as shown in the diagram below.

The coordinates of a pod,  are given by    where and  are positive constants. Ground level is represented by the line with equation y=-62.

Write down the values of and .

Find the height above the ground of a passenger pod when  radians.

Find the angle , to three significant figures, for a passenger pod located at the point .

What would you be able to say about the Ferris wheel in the case where ?

A lifejacket falls over the side of a boat from a height of m above sea level.
The height,m , of the lifejacket above or below sea level   at time  seconds after falling, is modelled by the equation cos , where are  positive constants.

Write down the value of .

Briefly explain how the constant affects the height of the lifejacket over time.

After 2.054 seconds the lifejacket is m below sea level. Find the value of  and determine whether the lifejacket is rising or sinking.

The number of daylight hours, , in the UK,  days after the spring equinox (the day in spring when the number of daylight hours is 12) is modelled using the function

sin 

where are  constants.

Write down the value of .

Given that the maximum number of daylight hours is 16.5, write down the value of .

For how many days of the year does the number of daylight hours remain below 10? Give your answer as a whole number of days.

If the spring equinox falls on the 21^st March, find the dates throughout the year when there are 16 hours of daylight.

The model needs to be adjusted every four years. Suggest a reason why.

The alternating voltage, , in an electrical circuit  seconds after it is switched on is modelled by the function

Express

in the form

sin 

where  are constants to be found.  and is  acute.

Find the voltage when the circuit is switched on.

The length of a spring, cm, at time  seconds, after being released from rest, is modelled by the function

cos

where and  are constants.

Describe the effect the constant has on the model.

Explain why the function would not be appropriate for modelling the length of a spring if .

The height above ground,m , of a drone used as part of an air display is modelled by the function sin , where is the time in seconds after launch  and  are constants.

The drone is launched upwards from a height of 23 m and  seconds later it reaches its maximum height of 26 m. The minimum height the drone reaches is 14 m.
Find the value of the constants ,,and  given that  is acute.

The drone’s lights switch off when its height drops below 17 m.
Show that the drone’s lights are on for two-thirds of its flight.

A swing boat fairground ride is modelled as moving forwards and backwards along the path of a semi-circle, radius m, as shown in the diagram below.

Show that, for ,

the -coordinate of the boat is given by  sin ,

the -coordinate is given by  cos .

The model is refined so that the coordinates of the boat can be calculated from the time, seconds, after the boat is set in motion.  The and  coordinates are now given by

sin 

where  is a constant.

Briefly explain why the modulus of cos is required for the - coordinate.

Given that the time between the boat reaching its maximum height at either end of the ride is 8 seconds, find the value of .

For , find the times when the boat is equidistant from the ground and horizontally from the origin.

The height of water, m , in a reservoir is modelled by the function

sin 

where  is the time in hours after midnight. and  are positive constants.

Briefly explain how each of the constants and affect the height of the water in the reservoir.

Show that the height of water will first be at its minimum level at time

hours after midnight.

Show that the rate of change of the height of water in the reservoir is at its greatest every

hours after midnight.

Engineers are designing a Ferris wheel with  passenger “pods”.
The wheel is modelled as a circle with centre  and radius meters.

One of the pods is to be located at the point with coordinates .

The thick lines on the diagram represent two symmetrical ground supports for the Ferris wheel each going from its centre to ground level.

The left-hand support is represented by the equation  .
The -axis represents ground level.

The  pods are to be evenly distributed around the wheel.
Ideally the engineers would like no more than three pods to be within the intersection of the supports at any one time. Find the maximum value of this design approach allows.

For both strength and aesthetic reasons, both the ground supports will be made in two sections. Thinner materials will be used within the wheel so as not to obstruct the view of, and from, the Ferris wheel and thicker material will be used for the lower base supports outside the wheel.

Find the percentage of the thicker material required.

The height, m, of a helicopter,  seconds after take-off, is modelled by the function

tan

The time lag between the pilot firing up the helicopter and leaving the ground is accounted for in the model by negative values of  for the period .

Find the value of α to two significant figures.

Show that the helicopter rises just 4 m between the times of seconds and   seconds

Find the height of the helicopter at the point at which the model ceases to be valid.

The number of daylight hours, , in the UK,  days after the spring equinox (the day in spring when the number of daylight hours is 12) is modelled using the function

where and  are constants.

Explain the meaning of the constants  and  in the context of this model.

During a normal year (not a leap year), the maximum number of daylight hours is
16 hours and 38 minutes.

Find the total number of daylight hours in the first half of the year.
(Assume a year in this sense starts on the spring equinox, when .
Give your answer to the nearest 10 hours.

The alternating voltage, , in a domestic electrical circuit,  seconds after it is switched on is modelled by the function

sin cos

Express

sin cos

in the form

sin 

where and  are constants to be found.   and is α acute.

In the UK, domestic electricity runs at a frequency, , of 50 Hertz (Hz).

The constant , is given by .