- #1

Kalibasa

- 21

- 0

## Homework Statement

It was just a basic work problem:

The two ropes seen in the figure below are used to lower a 245 kg piano 6.0 m from a second-story window to the ground. How much work is done by each of the three forces? (T1 = 1910 N andT2 = 1140 N)

There was a diagram with the angles labeled, and I got the right answers:

w: 14406 J

T1: -9925 J

T2: -4837 J

## Homework Equations

W= Fcos(theta)d

Fnet

_{y}= T1

_{y}+ T2

_{y}- w

## The Attempt at a Solution

Actually I got the problem right- T1 and T2 perform negative work and w performs positive work. But when I tried calculating the net force I found that it pointed upwards. This seems contradictory, since the piano has a displacement downwards. How can you have a net force opposite the displacement?

I guessed that if the net force pointed downwards too the weight would be exceeding the tension forces and the ropes would snap; in other words, you have to have a net force upwards so that the tension forces are strong enough to keep the piano in place. Is that right? But then I don't know where the displacement is coming from. Would you say that the piano is in dynamic equilibrium and that it's only moving because you're increasing the length of the ropes?

I'm confused...