6 A car of mass 1400 kg travelling at a speed of \(v \mathrm {~m} \mathrm {~s} ^ { - 1 }\) experiences a resistive force of magnitude \(40 v \mathrm {~N}\). The greatest possible constant speed of the car along a straight level road is \(56 \mathrm {~m} \mathrm {~s} ^ { - 1 }\).

1. Find, in kW , the greatest possible power of the car's engine.
2. Find the greatest possible acceleration of the car at an instant when its speed on a straight level road is \(32 \mathrm {~m} \mathrm {~s} ^ { - 1 }\).
3. The car travels down a hill inclined at an angle of \(\theta ^ { \circ }\) to the horizontal at a constant speed of \(50 \mathrm {~m} \mathrm {~s} ^ { - 1 }\). The power of the car's engine is 60 kW . Find the value of \(\theta\).