2. A car of mass 1 tonne is climbing a hill inclined at an angle \(\theta\) to the horizontal where \(\sin \theta = \frac { 1 } { 7 }\). When the car passes a point \(X\) on the hill, it is travelling at \(20 \mathrm {~m} \mathrm {~s} ^ { - 1 }\). When the car passes the point \(Y , 200 \mathrm {~m}\) further up the hill, it has speed \(10 \mathrm {~ms} ^ { - 1 }\). In a preliminary model of the situation, the car engine is assumed only to be doing work against gravity. Using this model,

1. find the change in the total mechanical energy of the car as it moves from \(X\) to \(Y\).
   (6 marks)
   In a more sophisticated model, the car engine is also assumed to work against other forces.
2. Write down two other forces which this model might include.
   (2 marks)