Answer to Question #95377 in Mechanics | Relativity for Pappu kumar gupta

Question

Given m=20kg,s=3m,f=150N,angle=30degree and myu=0.3 find work

Answer 1

If we need to find the work done by someone who applies the force of 150N, it will be

$$A_F=Fs\text{ cos}\alpha=150\cdot3\cdot\text{cos}30^\circ=389.71\text{ J}.$$

However, if we are to determine the work done by friction, it will be

$$A_f=fs=\mu Ns=\mu(mg-F\space\text{sin}\alpha)s=108.9\text{ J},$$

since the force has a component oriented upward while the force of gravity is directed downward, and the force of friction is defined by the normal force, i.e. the difference between the force of gravity and the vertical component of the force of 150 N.