A box is at rest in a rugged horizontal surface. The static friction coefficient between box and surface is μs = 0.5. A force is applied to the box in a direction 60° above the horizontal. The minimum magnitude of the force to get the box sliding is 520 N.

a. Find out the mass of the box.

b. If the box starts sliding with an acceleration of 1.4 m/s2 under the minimum magnitude of the force mentioned above, what must be the kinetic friction coefficient between box and surface?