A block is resting on an incline plane. The block just starts slipping when the angle of the plane is increased to 30⁰. The co-efficient of friction is

1. 0.5
2. 
3. 
4. 

A block of mass 5 kg is resting on a horizontal rough surface. The coefficient of friction between the block and the surface is 0.2. If pulled by a horizontal force of magnitude 10 N, the friction force will be

1. 10 N