Is My Solution to the Grade 11 Physics Problem Correct?

[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.

 

[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.

At any rate, your answer is correct.

 

[NascentOxygen]

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!

 

[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.