The frictional force is oposing the force that we apply to this mass. Therefore the overall force is [tex]F_{total}=F_{applied}-F_{friction}=20-15 =5 (Newton)[/tex]
The second principle of physics tells us that the acceleration of a mass is direct proportional to the applied force, the mass of that object being the proportionality constant.
[tex]F=m*a[/tex]
Hence [tex]a= \frac{F}{m}=5/10 =0.5 (m/s^2) [/tex]
