6 A block, of mass 5 kg , slides down a rough plane inclined at \(40 ^ { \circ }\) to the horizontal. When modelling the motion of the block, assume that there is no air resistance acting on it.
- Draw and label a diagram to show the forces acting on the block.
- Show that the magnitude of the normal reaction force acting on the block is 37.5 N , correct to three significant figures.
- Given that the acceleration of the block is \(0.8 \mathrm {~m} \mathrm {~s} ^ { - 2 }\), find the coefficient of friction between the block and the plane.
- In reality, air resistance does act on the block. State how this would change your value for the coefficient of friction and explain why.