A 0.5 kg block is moving at constant speed on a horizontal surface. the friction force acting on the block is 20N, calculate uk

The friction force is equal to the normal force by the object equal to the weight of the object multiplied by the coefficient of friction. In this case, we substitute to the equation

4.9 N * 9.8 m/s2 = 20 N * ukuk is equal then to 0.245.