Auniform 2.50m ladder of mass 7.30kg is leaning against a vertical wall while making an angle of 51.0degree with the floor. a worker pushes the ladder up against the wall until it is vertical.
a)how much work did this person do against gravity?

19.95 J

Explanation:

The center of mass of the ladder is initially at a height of:

The center of mass of the ladder ends at a height of:

=L/2

So, the work done is equal to the change in potential energy which is:

W = PE =

now

therefore

W = [mgL/2]×[1 - sin(theta)]

W = [(7.30)(9.81)(2.50)/2]×[1-sin(51°)]

solving this we get

W = 19.95 J

statement #3 on andre"s list is false.