The surface exerts an upward normal force N such that the net vertical force on the mass is
∑ F = N - mg = 0
where m = 2 kg and g is the acceleration due to gravity. So
N = (2 kg) (9.8 m/s²) = 19.6 N
The frictional force then has magnitude µ (19.6 N), where µ is the coefficient of static friction. If the maximum magnitude of static friction is to be 10 N, we have
10 N = µ (19.6 N)
===> µ = (10 N)/(19.6 N) ≈ 0.51
