Ahahaha this exact question was in my tuition homework, what a coincidence
Okay so
a) The force acting on object A is simply the force due to gravity. F = ma = (30)(9.8) = 294N towards centre of Earth
b) Use the formula: Height = (initial y velocity)(time) + 1/2(y acceleration)(t^2)
25 = 0 + 4.9t^2
t^2 = 25/4.9
t = 2.3s (2s.f)
c) For object A, at it's maximum height, the only vertical force is the force due to gravity, which is 294N towards centre of Earth. For object B however, there is a centripetal force acting on the object. There is also a force due to gravity(which is cancelled out by the reaction force of the pivot arm) and another force due to the tension of the pivot arm.
Those responses would get you full marks
