Work Done by Weight Homework: Find W

[Legerity]

Homework Statement

A 700 kg crate is on a rough surface inclined at 30°. A constant external force P = 5600 N is applied horizontally to the crate. The force pushes the crate a distance of 3.0 m up the incline, in a time interval of 7.3 s, and the velocity changes from v1 = 1.4 m/s to v2 = 2.5 m/s. What is the work done by weight?

Homework Equations

W = Fd, KE = 0.5mv^2, PE = mgh

The Attempt at a Solution

I drew the free-body diagram, but I am stumped on how to go about the problem. What is the work done by weight, and how can I find it? I don't exactly know what it is.

 

[haruspex]

I don't know what they mean by 'work done by weight'. My guess is they meant the work done by the force P. (Cut and paste error from another question?)

 

[Legerity]

I don't know what they mean by 'work done by weight'. My guess is they meant the work done by the force P. (Cut and paste error from another question?)

I figured out the problem, and it is the work done by gravity on the box (ΔPE).

 

[haruspex]

I figured out the problem, and it is the work done by gravity on the box (ΔPE).

Really? So most of the information is irrelevant? (Or maybe there are more parts to the question?)

 

[Legerity]

Really? So most of the information is irrelevant? (Or maybe there are more parts to the question?)

Yes, there is another part of the question I am stuck on. It is now asking me to find the work done by the frictional force, and my attempts at the problem have been futile. The only things changed in the info in the original post is that now V2 = 2.3 m/s, and time = 8.3 s. Could you possibly help?

 

[PhizKid]

You'll have to use an equation that relates conservation of energy and the energy lost by friction: [itex]KE_{i}+PE_{i}+WE_{i}=KE_{f}+PE_{f}+WE_{f}[/itex]

 

[haruspex]

It is now asking me to find the work done by the frictional force,

You know the distance, so it remains to calculate the frictional force. What equations do you get from your free body diagram?

 

[PhanthomJay]

I figured out the problem, and it is the work done by gravity on the box ( - ΔPE).

see important correction in red.