# Grade 11 high school physics question

1. Jun 5, 2014

### taotao

Find the acceleration of the system

Ff= u(Fn)
Fnet=ma

I would just like to know if the way that I solved this problem is correct.

2. Jun 5, 2014

### Nathanael

Yes, if you estimate g to be $10\frac{m}{s^2}$ instead of $9.8\frac{m}{s^2}$ then this is correct.

(Assuming there's no friction between the 20N weight and the side)

EDIT:
It kind of looks like you said the 5N weight was a part of the frictional force, which isn't true.

3. Jun 6, 2014

### Staff: Mentor

Yes, the second line of working is wrong---for two reasons. The only friction force here is the 4N.

An equals sign means exactly that, viz, "equals". You have misused it on that line.

Apart from those matters, it looks good!

4. Jun 6, 2014

### dauto

You wrote 10 x 0.4 = 4+5 which is not correct. As a teacher I do take points away from my students when they do that even if they get the correct equation at the end. Always make sure that every equation you write on the paper is correct.

Tip: Don't just write down the steps you took when using the calculator. That doesn't work.