2 A slide at a water park may be modelled as a smooth plane of length 20 metres inclined at \(30 ^ { \circ }\) to the vertical. Anne, who has a mass of 55 kg , slides down the slide. At the top of the slide, she has an initial velocity of \(3 \mathrm {~m} \mathrm {~s} ^ { - 1 }\) down the slide.

1. Calculate Anne's initial kinetic energy.
2. By using conservation of energy, find the kinetic energy and the speed of Anne after she has travelled the 20 metres.
3. State one modelling assumption which you have made.