Calculating Work on a Slope with Friction Coefficient of 0.2

[fsxadder]

Homework Statement

An object of mass 3kg is sliding down a slope with a friction coefficient of 0.2. The distance over which it slides down before it hits the ground is 7m. Write down an expression for work peformed on the object over the seven metres as a function of the angle X that the slope makes with the horizontal.

The angle X is between the hill and the horizontal with the object on the hill.

Homework Equations

Frictional coefficent
Work

The Attempt at a Solution

Ive tried multiple times and i keep getting stuck at the angle part. If anyone could go through the whole calculation so i can cross reference would be great. Please!

 

[Doc Al]

Show the details of your calculation so far. How do you find the force of friction?

 

[fsxadder]

Show the details of your calculation so far. How do you find the force of friction?

The frictional coefficient given is 0.2 I put that into the frictional coefficient equation but is not making sense.

First i was going to find the two components of the Weight and the horizontal force

Then Fs.

Then Fn

But i don't know how to. Please show!

 

[Doc Al]

You need to learn how to find the components of the weight parallel and perpendicular to the incline. Read this: http://www.physicsclassroom.com/Class/vectors/u3l3e.cfm"

 

[fsxadder]

Ive calculated that the expression for work performed on an object over a distance as a function of Angle X.

205.8*(sin(X) - 0.2* cos(X) ) J

I now need to calculate, presuming with the above worked out, the energy lost at the following angles:

10 degrees
20 degrees
30 degrees

(These angles are the angles that the slope makes with the horizontal)
The mass of the object is 3kg
The length of the slope is 7m

 

[Doc Al]

Ive calculated that the expression for work performed on an object over a distance as a function of Angle X.

205.8*(sin(X) - 0.2* cos(X) ) J

This gives you the net work done by all forces acting on the object. Is that what you're asked to find?

I now need to calculate, presuming with the above worked out, the energy lost at the following angles:

10 degrees
20 degrees
30 degrees

By 'energy lost' do you mean the work done by friction?

 

[fsxadder]

This gives you the net work done by all forces acting on the object. Is that what you're asked to find?

They're asking me to write an expression for the work performed on the object over the 7m as a function of the angle X.

By 'energy lost' do you mean the work done by friction?

The Energy Lost is referring to the ENERGY LOST DUE TO FRICTION

 

[Doc Al]

They're asking me to write an expression for the work performed on the object over the 7m as a function of the angle X.

Work performed by what force? All forces? If so, your expression does that.

The Energy Lost is referring to the ENERGY LOST DUE TO FRICTION

OK, just calculate the work done by friction.

 

[fsxadder]

OK, just calculate the work done by friction.

How would i do that?

Would use this equation:

W = F(f) x d

How would i calculate F(f)

Im literllay begging for an an explanation here,r please.

 

[Doc Al]

How would i do that?

How did you arrive at the expression you posted? That contains the work done by friction.

Would use this equation:

W = F(f) x d

Yes.

How would i calculate F(f)

Start by calculating the normal force.