## A Climate Aware Citizen

A person decides in 2020 that they want to completely eradicate their carbon footprint in 20 months.

Following this decision, they begin to use multiple technologies that decrease their carbon footprint, such as limiting air travel, carbon offsetting and a solar powered home that contributes energy back to the national grid.

This results in their rate of emissions per month, E, following the equation

$E = 12\ln\left( t + 5 \right) – 2t + 2$

where t is the time, in months, since 2020.

a) Show that they achieve zero emissions between 18 and 22 months after they start.

[2 marks]

b) Using the iteration formula $$t_{n + 1} = 6\ln{(t + 5)} + 1$$ with $$t_{o} = 18$$, find the value of $$t$$ at which they achieve zero emissions to 2 decimal places.

[3 marks]

## Internal combustion engines

A country’s government wants to reduce the number of cars using internal combustion engines by encouraging the purchase of electric vehicles.

The total number of cars using internal combustion engines in a country at time t can be modelled by the equation

$N\left( t \right) = \left( 3.5 \times 10^{7} + E \right)e^{- \frac{1}{10}t} – E$

Where N(t) is the number of cars using internal combustion engines at time t years after the program was introduced and E is the number of electric vehicles on the roads before the government initiative.

Using the equation for this model,

a) Explain the significance of the number 3.5 x 107.

[1 mark]

b) Explain why the initial number of cars using internal combustion engines is independent of the initial number of electric vehicles.

[2 marks]

c) Calculate the number of cars using internal combustion engines after 10 years if the initial number of electric vehicles is 2 x 106.

[2 marks]

d) Analyse the suitability of this model by evaluating it for large values of t.

[2 marks]

## A Solar Sine Curve

You are given the equation

$f\left( x \right) = 5\cos\theta – 8\sin\theta$

a) Express f(x) in the form $$R\cos{(\theta + \alpha})$$ where $$R > 0$$ and$$\ 0 < \alpha < \pi$$. Write R in surd form and give the value of α correct to 4 decimal places.

[4 marks]

The temperature of a solar panel, T ˚C, can be modelled by the equation

$T = 20 + 5\cos\frac{4x}{15} – 8\sin\frac{4x}{15}\ ,\ 0 \leq x \leq 72$

Where x is the time in hours since 10pm one evening?

b) Calculate the maximum value of T predicted by this model and the value of x, to 2 decimal places, when this value first occurs.

[4 marks]

c) Calculate the times during the first 24 hours when the temperature is predicted, by this model, to be exactly 17 ˚C

[4 marks]

## A New Renewable

A scientist wishes to develop a new way of generating renewable energy.

They decide to use a large magnet on a large spring, oscillating through a coil of wire, generating a current that could then charge a battery, which in turn would store the energy released from the system.

The system is set into motion with a winch system that can be used to set the spring. The following equation can then be used to describe the oscillations, in metres, t minutes after it has been set into motion:

$A = 10e^{- 0.05t}\cos{10t}$

a) On a plot of A against t, show that the t values of the
turning points satisfy the equation $$\tan{10t} = – \frac{1}{200}$$

[4 marks]

The battery can only be charged when the amplitude of the oscillations of the spring are greater than 1m. The amplitudes, A, of the oscillations are found at the turning points of the curve.

b) Give the t value of the last turning point where |A|≥1m, and the battery can no longer be charged.

[4 marks]

## Net-Zero Buses

15 cities, each of varying sizes, decide to have carbon-neutral public transport systems.

When the cities are arranged in size order from smallest to largest, the number of new electric buses they need follows an arithmetic sequence with first term (representing the smallest amount of buses needed for the smallest city) a buses and common difference d buses.

The 7ᵗʰ city in this progression needs 580 new electric buses and the largest city needs 1020 new electric buses.

Find the value of a and the value of d.

[5 marks]

## EV Increase

A country decides to subsidise the purchase of electric vehicles, causing more people to buy them.

Initially, the country used an equivalent of 56 million tonnes of oil for transport.

Since the government subsidy, the transport sector in each subsequent year has required 80% of the amount of oil that the previous year required.

a) Write a recurrence relation to model the amount of oil used, in million tonnes, in each subsequent year.

[2 marks]

b) Find the amount of oil needed for the transport sector after the fifth year.

[2 marks]

c) Find the total amount of oil used until the transport sector requires no more oil.

[4 marks]

d) State one limitation with the model.

[1 mark]

## A Nuclear Disaster

Chernobyl is the site of a nuclear disaster that happened in 1986.

Due to the slow decay of radioactive elements, the site is still extremely dangerous today.

In 2016, engineers covered the main damaged nuclear reactor with a giant concrete cap, as shown below:

The cross section of this cover can be modelled with the parametric equations:

$x = 8\left( t + 10 \right)\ ,\ y = 100 – t^{2}\ ,\ – 19 \leq t \leq 10$

a) Find the Cartesian equation of this model.

[3 marks]

b) The width of the cap, according to the model.

[2 marks]

## Warming up a Solar Cell

The temperature T˚C of a solar cell during a 24 hour period is modelled as

$T = 20 – k\left( 15 – \frac{5t}{4} \right)^{2}\ ,\ \ \ 0 \leq t \leq 24$

Where t is the time in hours after midnight and k is a positive constant

The temperature of the solar cell at midnight is 5˚C.

a) Use this information to find the value of k in the model.

[2 marks]

b) Find, according to the model, the temperature of the solar cell at 8:30 am.

[2 mark]

c) Determine the greatest temperature of the solar cell and the time at which this temperature occurs.

[3 marks]

d) State one limitation of the model

[1 mark]

## Solar Panelling a House

A homeowner wishes to cover their roof with solar panels.

Their roof can be modelled as a prism with volume 24m3

The height of the triangular cross section is h.

If solar panels can only be placed on the 2 rectangular sections of the roof

a) Work out the area of roof that could be covered by solar panels. Give your answer to 2.s.f.

[4 marks]

A company provides solar panels that are 1.5m long and 1.0m high and cost £200 each, including installation.

b) If this is the only size of solar panels available, how much will it cost the homeowner to buy and install them?

[3 marks]

## An Offshore Wind Farm

Below is a diagram of 3 offshore wind turbines, A, B and C, in a wind farm, as seen from above.

Given that the bearing from turbine C to turbine B is 90˚, and the distance from turbine A to turbine B is 3 km

Calculate the distances AC and CB.

[4 marks]