A motorcycle and 60.0 kg rider accelerate at 3.0 m/s^2 up a ramp inclined 10 degrees above the horizontal. (a) What is the magnitude of the net force acting on the rider? (b) What is the magnitude of the force on the rider from the motorcycle?
Net Force = Mass x Acceleration
Answer given for first part: 180 N
Answer given for second part: 640 N
The Attempt at a Solution
The first part is easily solved: Since the mass is given to be 60 kg, and the acceleration up the incline is 3 m/s^2, therefore the net force is 60 x 3 = 180 N. This matches the answer given.
For the second part, I thought it could be done by taking the normal force acting on the motorcycle, which on the given incline, would be = mg cos 10 degrees = 60 x 9.8 x cos 10 degrees = 579 N.
This is way off the answer given, which is 640 N. Did I get some theoretical bit wrong? I really don't see any other force which should be acting - after all, the mass of the motorcycle is not given.