Physics help please!!!?

Question

A person opens a door by applying a 15N force to the door at a distance .90m from the hinges. The door opens 120 degree in 2.0s. How much work was done?

Answer 1

The force applied to the door at some distance away from the center of rotation is a torque [force].

T = F * r
where T is the Torque, F is the force applied, and r is the radial distance away from the center which the torque is applied.

When a torque is applied over an angular displacement work is done,
W = T * (delta theta)
Where W is the work done, T is the torque, and (delta theta) is the angular displacement which occurs.
In this case the angular displacement (delta theta) is how much the door opens (120 degrees), although this amount must be measured in radians, not degrees.

To convert degrees to radias,
Radians = degrees * pi / 180

So to answer this problem convert 120 degrees into radians,
radians = 120 * pi / 180
radians = 2.09 radians

Then find the torque,
T = F * r
T = 15 N * .9 m
T = 13.5 N m

Now plug these values into the work equation,
W = T * (delta theta)
W = 13.5 N m * 2.09 radians
W = 28.215 Joules

Answer 2

W = F * d

F = 15N

d = (0.90m * 2 * pi) * (120/360)

Do the math, and you're straight. The time is irrelevant information. You can use the time to find the power that needed to be exerted, but that's irrelevant to finding the work done.