A uniform meter stick of mass 0.60kg is pivoted about one end so it can rotate freely in a vertical plane. A small 0.40kg mass is firmly attached to the free end of the stick. Immediately after a perpendicular force is applied at the midpoint of the stick (exactly 0.50m from the pivot), the system rotates with an angular acceleration of 4.0rads−2. Neglect gravity during the instant the force is applied. What is the magnitude of the applied force?
a) 2.4N
b) 6.4N
c) 4.8N
d) 3.6N