A man begins to climb up a 12-ft ladder . The man has mass 80 kg, while
the ladder has mass 10 kg. The wall against which the ladder rests is very smooth,
which means that the tangential (vertical) component of force at the contact between
ladder and wall is negligible. The foot of the ladder is placed 6 ft from the wall. The
ladder, with the man’s weight on it, will slip if the tangential (horizontal) force at the
contact between ladder and ground exceeds 350 N. How far up the ladder can the
man safely climb?