1. Nov 3, 2007

### jcksn34

just wanted to know if anyone else is using the program mastering physics for homework and getting wrong answers to the questions. This has happened to me a few times and im sure their answers are completely wrong. For example a simple work problem with a force pushing a block up a ramp. when asked for the work in joules of friction force you find first the normal force multiply that by the coefficient of friction then substitute in the formula W=F times displacement times cos theta correct? And normal force is perpendicular to the plane of the incline. For example the explaination of their answer normal force of a 1 kg box being pushed up an incline was equal to 9.8N? which is not right if normal force is perpendicular the plane of the incline. am i crazy or is this program giving wrong answers?

2. Nov 3, 2007

### gills

Copy and paste the problem in here, and people will be able to judge it better. The chances of mastering physics having wrong answers is very rare.

3. Nov 3, 2007

### G01

I disagree gills. I tutor General Physics at my university and I have had problems with Mastering Physics as well. It's not out of the question for Mastering Physics to have wrong answers. I have seen it myself. It is also very strict with units. Make sure all your data is given in SI units and make sure it wants the answer in SI units!

I am no fan of Mastering Physics either! Good luck putting up with it!

4. Nov 3, 2007

### jcksn34

A block of mass 1.00kg sits on an inclined plane as shown. A force of magnitude 100N is pulling the block up the incline at constant speed. The coefficient of kinetic friction between the plane and the block is 0.500. The inclined plane makes an angle 30.0 degrees with the horizontal.

What is the total work done on the block by the force of friction as the block moves a distance 8.00 up the incline?

mastering physics answer = -39.2 joules

Mastering physics explaination=
Hint 1. Find the magnitude of the normal force

What is the magnitude of the normal force?
Hint 1. How to find the normal force
Consider all the forces that have a non-zero component along the direction perpendicular to the slope. There are only two such forces: the weight of the block and force .
What is the magnittude of the component of the weight perpendicular to the slope? Draw the axes and label the angles clearly to find out.

=9.80N

=4.90

5. Nov 3, 2007

### G01

The normal force in this case should be:

$$F_N = mg \cos(30^o)=9.8(.866)=8.48N$$

Yeah, I think Mastering Physics screwed up here.

6. Nov 3, 2007

### jcksn34

thank you, thats what i got too, now i know to double check their answers if im unsure instead of wasting a half hour trying to figure out how to get a wrong answer lol!