Aplank of length 2l leans against a wall. it starts to slip downward without friction. show that the top of the plank loses contact with the wall when it is at two-thirds of its initial height.

as a general rule, scissors have blades less than 6 in (15 cm) long and usually have handles with finger holes of the same size. shears have blades scissors used to cut hair or fabric must be much sharper.

i don't understand. explain it clearly