a small canon is placed on top of a fortification the cannon ball leaves the muzzle of the canon with a speed of 85 m/s

Yup no bull frogs here man

If its history of, then b) because a) implies only present day (now)

2.77 x 10^-3 its for plato user 

I'm having some difficulty seeing the diagram clearly.but the question says there's a net inward force on the object.so we know right away,  from newton's 2nd law of motion, thatthat baby is accelerating.  it doesn't even matter which way thenet force is pointing.  if there's any net force, then either theobject's speed or else its direction must be changing.