4 A lorry of mass 25000 kg travels along a straight horizontal road. There is a constant force of 3000 N resisting the motion.
- Find the power required to maintain a constant speed of \(30 \mathrm {~m} \mathrm {~s} ^ { - 1 }\).
The lorry comes to a straight hill inclined at \(2 ^ { \circ }\) to the horizontal. The driver switches off the engine of the lorry at the point \(A\) which is at the foot of the hill. Point \(B\) is further up the hill. The speeds of the lorry at \(A\) and \(B\) are \(30 \mathrm {~m} \mathrm {~s} ^ { - 1 }\) and \(25 \mathrm {~m} \mathrm {~s} ^ { - 1 }\) respectively. The resistance force is still 3000 N . - Use an energy method to find the height of \(B\) above the level of \(A\).