# Graph explanation for force and friction

Question: A block of mass $$m$$ is placed on an inclined plane with angle of inclination $$\theta$$. Let $$N$$, $$f_L$$ and $$F$$ respectively represent the normal reaction, limiting force of friction and the net force down the inclined plane. Let $$\mu$$ be the coefficient of friction. The dependence of $$N$$,$$f_L$$ and $$F$$ on $$\theta$$ is indicated by plotting graphs as shown below. Then curves (1), (2) and (3) respectively represent _____ respectively.

Answer:$$F$$,$$N$$ and $$f_L$$

I need an explanaton

• Just examine the end points. At $\theta = 0$, flat plane, what would you expect the net force to be? At $\theta = 90$, vertical plane, what would you expect the normal to be? Etc... – npojo Mar 16 '18 at 10:38

Consider how the component of the weight of the block is related to the angle of inclination $\theta$ and also how the normal reaction force relates to the angle $\theta$.
Remember that the limiting friction force is proportional to the normal reaction with the constant of proportionality being the coefficient of static friction $\mu_{\rm static}$ which is usually less than one.