4. A cyclist and her bicycle have a combined mass of 78 kg . While riding on level ground and using her greatest driving force, she is able to accelerate uniformly from rest to \(10 \mathrm {~ms} ^ { - 1 }\) in 15 seconds against constant resistive forces that total 60 N .

1. Show that her maximum driving force is 112 N . The cyclist begins to ascend a hill, inclined at an angle \(\alpha\) to the horizontal, riding with her maximum driving force and against the same resistive forces. In this case, she is able to maintain a steady speed.
2. Find the angle \(\alpha\), giving your answer to the nearest degree.
3. Comment on the assumption that the resistive force remains constant
   1. in the case when the cyclist is accelerating,
   2. in the case when she is maintaining a steady speed.
      (2 marks)